US10252707B2 - Brake control system, brake system, and brake hydraulic pressure generating method - Google Patents

Brake control system, brake system, and brake hydraulic pressure generating method Download PDF

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US10252707B2
US10252707B2 US15/300,875 US201415300875A US10252707B2 US 10252707 B2 US10252707 B2 US 10252707B2 US 201415300875 A US201415300875 A US 201415300875A US 10252707 B2 US10252707 B2 US 10252707B2
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hydraulic line
brake
hydraulic
pressure
chamber
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US20170015293A1 (en
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Hideaki YAGASHIRA
Hiroki Sonoda
Asahi Watanabe
Toshiya Oosawa
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Hitachi Astemo Ltd
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Hitachi Automotive Systems Ltd
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    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B60—VEHICLES IN GENERAL
    • B60T—VEHICLE BRAKE CONTROL SYSTEMS OR PARTS THEREOF; BRAKE CONTROL SYSTEMS OR PARTS THEREOF, IN GENERAL; ARRANGEMENT OF BRAKING ELEMENTS ON VEHICLES IN GENERAL; PORTABLE DEVICES FOR PREVENTING UNWANTED MOVEMENT OF VEHICLES; VEHICLE MODIFICATIONS TO FACILITATE COOLING OF BRAKES
    • B60T13/00—Transmitting braking action from initiating means to ultimate brake actuator with power assistance or drive; Brake systems incorporating such transmitting means, e.g. air-pressure brake systems
    • B60T13/10—Transmitting braking action from initiating means to ultimate brake actuator with power assistance or drive; Brake systems incorporating such transmitting means, e.g. air-pressure brake systems with fluid assistance, drive, or release
    • B60T13/12—Transmitting braking action from initiating means to ultimate brake actuator with power assistance or drive; Brake systems incorporating such transmitting means, e.g. air-pressure brake systems with fluid assistance, drive, or release the fluid being liquid
    • B60T13/14—Transmitting braking action from initiating means to ultimate brake actuator with power assistance or drive; Brake systems incorporating such transmitting means, e.g. air-pressure brake systems with fluid assistance, drive, or release the fluid being liquid using accumulators or reservoirs fed by pumps
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B60—VEHICLES IN GENERAL
    • B60T—VEHICLE BRAKE CONTROL SYSTEMS OR PARTS THEREOF; BRAKE CONTROL SYSTEMS OR PARTS THEREOF, IN GENERAL; ARRANGEMENT OF BRAKING ELEMENTS ON VEHICLES IN GENERAL; PORTABLE DEVICES FOR PREVENTING UNWANTED MOVEMENT OF VEHICLES; VEHICLE MODIFICATIONS TO FACILITATE COOLING OF BRAKES
    • B60T13/00—Transmitting braking action from initiating means to ultimate brake actuator with power assistance or drive; Brake systems incorporating such transmitting means, e.g. air-pressure brake systems
    • B60T13/10—Transmitting braking action from initiating means to ultimate brake actuator with power assistance or drive; Brake systems incorporating such transmitting means, e.g. air-pressure brake systems with fluid assistance, drive, or release
    • B60T13/66—Electrical control in fluid-pressure brake systems
    • B60T13/662—Electrical control in fluid-pressure brake systems characterised by specified functions of the control system components
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B60—VEHICLES IN GENERAL
    • B60T—VEHICLE BRAKE CONTROL SYSTEMS OR PARTS THEREOF; BRAKE CONTROL SYSTEMS OR PARTS THEREOF, IN GENERAL; ARRANGEMENT OF BRAKING ELEMENTS ON VEHICLES IN GENERAL; PORTABLE DEVICES FOR PREVENTING UNWANTED MOVEMENT OF VEHICLES; VEHICLE MODIFICATIONS TO FACILITATE COOLING OF BRAKES
    • B60T13/00—Transmitting braking action from initiating means to ultimate brake actuator with power assistance or drive; Brake systems incorporating such transmitting means, e.g. air-pressure brake systems
    • B60T13/10—Transmitting braking action from initiating means to ultimate brake actuator with power assistance or drive; Brake systems incorporating such transmitting means, e.g. air-pressure brake systems with fluid assistance, drive, or release
    • B60T13/12—Transmitting braking action from initiating means to ultimate brake actuator with power assistance or drive; Brake systems incorporating such transmitting means, e.g. air-pressure brake systems with fluid assistance, drive, or release the fluid being liquid
    • B60T13/14—Transmitting braking action from initiating means to ultimate brake actuator with power assistance or drive; Brake systems incorporating such transmitting means, e.g. air-pressure brake systems with fluid assistance, drive, or release the fluid being liquid using accumulators or reservoirs fed by pumps
    • B60T13/142—Systems with master cylinder
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B60—VEHICLES IN GENERAL
    • B60T—VEHICLE BRAKE CONTROL SYSTEMS OR PARTS THEREOF; BRAKE CONTROL SYSTEMS OR PARTS THEREOF, IN GENERAL; ARRANGEMENT OF BRAKING ELEMENTS ON VEHICLES IN GENERAL; PORTABLE DEVICES FOR PREVENTING UNWANTED MOVEMENT OF VEHICLES; VEHICLE MODIFICATIONS TO FACILITATE COOLING OF BRAKES
    • B60T13/00—Transmitting braking action from initiating means to ultimate brake actuator with power assistance or drive; Brake systems incorporating such transmitting means, e.g. air-pressure brake systems
    • B60T13/10—Transmitting braking action from initiating means to ultimate brake actuator with power assistance or drive; Brake systems incorporating such transmitting means, e.g. air-pressure brake systems with fluid assistance, drive, or release
    • B60T13/12—Transmitting braking action from initiating means to ultimate brake actuator with power assistance or drive; Brake systems incorporating such transmitting means, e.g. air-pressure brake systems with fluid assistance, drive, or release the fluid being liquid
    • B60T13/14—Transmitting braking action from initiating means to ultimate brake actuator with power assistance or drive; Brake systems incorporating such transmitting means, e.g. air-pressure brake systems with fluid assistance, drive, or release the fluid being liquid using accumulators or reservoirs fed by pumps
    • B60T13/142—Systems with master cylinder
    • B60T13/145—Master cylinder integrated or hydraulically coupled with booster
    • B60T13/146—Part of the system directly actuated by booster pressure
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B60—VEHICLES IN GENERAL
    • B60T—VEHICLE BRAKE CONTROL SYSTEMS OR PARTS THEREOF; BRAKE CONTROL SYSTEMS OR PARTS THEREOF, IN GENERAL; ARRANGEMENT OF BRAKING ELEMENTS ON VEHICLES IN GENERAL; PORTABLE DEVICES FOR PREVENTING UNWANTED MOVEMENT OF VEHICLES; VEHICLE MODIFICATIONS TO FACILITATE COOLING OF BRAKES
    • B60T13/00—Transmitting braking action from initiating means to ultimate brake actuator with power assistance or drive; Brake systems incorporating such transmitting means, e.g. air-pressure brake systems
    • B60T13/10—Transmitting braking action from initiating means to ultimate brake actuator with power assistance or drive; Brake systems incorporating such transmitting means, e.g. air-pressure brake systems with fluid assistance, drive, or release
    • B60T13/66—Electrical control in fluid-pressure brake systems
    • B60T13/68—Electrical control in fluid-pressure brake systems by electrically-controlled valves
    • B60T13/686—Electrical control in fluid-pressure brake systems by electrically-controlled valves in hydraulic systems or parts thereof
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B60—VEHICLES IN GENERAL
    • B60T—VEHICLE BRAKE CONTROL SYSTEMS OR PARTS THEREOF; BRAKE CONTROL SYSTEMS OR PARTS THEREOF, IN GENERAL; ARRANGEMENT OF BRAKING ELEMENTS ON VEHICLES IN GENERAL; PORTABLE DEVICES FOR PREVENTING UNWANTED MOVEMENT OF VEHICLES; VEHICLE MODIFICATIONS TO FACILITATE COOLING OF BRAKES
    • B60T17/00—Component parts, details, or accessories of power brake systems not covered by groups B60T8/00, B60T13/00 or B60T15/00, or presenting other characteristic features
    • B60T17/02—Arrangements of pumps or compressors, or control devices therefor
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B60—VEHICLES IN GENERAL
    • B60T—VEHICLE BRAKE CONTROL SYSTEMS OR PARTS THEREOF; BRAKE CONTROL SYSTEMS OR PARTS THEREOF, IN GENERAL; ARRANGEMENT OF BRAKING ELEMENTS ON VEHICLES IN GENERAL; PORTABLE DEVICES FOR PREVENTING UNWANTED MOVEMENT OF VEHICLES; VEHICLE MODIFICATIONS TO FACILITATE COOLING OF BRAKES
    • B60T17/00—Component parts, details, or accessories of power brake systems not covered by groups B60T8/00, B60T13/00 or B60T15/00, or presenting other characteristic features
    • B60T17/04—Arrangements of piping, valves in the piping, e.g. cut-off valves, couplings or air hoses
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B60—VEHICLES IN GENERAL
    • B60T—VEHICLE BRAKE CONTROL SYSTEMS OR PARTS THEREOF; BRAKE CONTROL SYSTEMS OR PARTS THEREOF, IN GENERAL; ARRANGEMENT OF BRAKING ELEMENTS ON VEHICLES IN GENERAL; PORTABLE DEVICES FOR PREVENTING UNWANTED MOVEMENT OF VEHICLES; VEHICLE MODIFICATIONS TO FACILITATE COOLING OF BRAKES
    • B60T7/00—Brake-action initiating means
    • B60T7/02—Brake-action initiating means for personal initiation
    • B60T7/04—Brake-action initiating means for personal initiation foot actuated
    • B60T7/042—Brake-action initiating means for personal initiation foot actuated by electrical means, e.g. using travel or force sensors
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B60—VEHICLES IN GENERAL
    • B60T—VEHICLE BRAKE CONTROL SYSTEMS OR PARTS THEREOF; BRAKE CONTROL SYSTEMS OR PARTS THEREOF, IN GENERAL; ARRANGEMENT OF BRAKING ELEMENTS ON VEHICLES IN GENERAL; PORTABLE DEVICES FOR PREVENTING UNWANTED MOVEMENT OF VEHICLES; VEHICLE MODIFICATIONS TO FACILITATE COOLING OF BRAKES
    • B60T8/00—Arrangements for adjusting wheel-braking force to meet varying vehicular or ground-surface conditions, e.g. limiting or varying distribution of braking force
    • B60T8/17—Using electrical or electronic regulation means to control braking
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B60—VEHICLES IN GENERAL
    • B60T—VEHICLE BRAKE CONTROL SYSTEMS OR PARTS THEREOF; BRAKE CONTROL SYSTEMS OR PARTS THEREOF, IN GENERAL; ARRANGEMENT OF BRAKING ELEMENTS ON VEHICLES IN GENERAL; PORTABLE DEVICES FOR PREVENTING UNWANTED MOVEMENT OF VEHICLES; VEHICLE MODIFICATIONS TO FACILITATE COOLING OF BRAKES
    • B60T8/00—Arrangements for adjusting wheel-braking force to meet varying vehicular or ground-surface conditions, e.g. limiting or varying distribution of braking force
    • B60T8/32—Arrangements for adjusting wheel-braking force to meet varying vehicular or ground-surface conditions, e.g. limiting or varying distribution of braking force responsive to a speed condition, e.g. acceleration or deceleration
    • B60T8/34—Arrangements for adjusting wheel-braking force to meet varying vehicular or ground-surface conditions, e.g. limiting or varying distribution of braking force responsive to a speed condition, e.g. acceleration or deceleration having a fluid pressure regulator responsive to a speed condition
    • B60T8/40—Arrangements for adjusting wheel-braking force to meet varying vehicular or ground-surface conditions, e.g. limiting or varying distribution of braking force responsive to a speed condition, e.g. acceleration or deceleration having a fluid pressure regulator responsive to a speed condition comprising an additional fluid circuit including fluid pressurising means for modifying the pressure of the braking fluid, e.g. including wheel driven pumps for detecting a speed condition, or pumps which are controlled by means independent of the braking system
    • B60T8/4004—Repositioning the piston(s) of the brake control means by means of a fluid pressurising means in order to reduce the brake pressure
    • B60T8/4009—Repositioning the piston(s) of the brake control means by means of a fluid pressurising means in order to reduce the brake pressure the brake control means being the wheel cylinders
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B60—VEHICLES IN GENERAL
    • B60T—VEHICLE BRAKE CONTROL SYSTEMS OR PARTS THEREOF; BRAKE CONTROL SYSTEMS OR PARTS THEREOF, IN GENERAL; ARRANGEMENT OF BRAKING ELEMENTS ON VEHICLES IN GENERAL; PORTABLE DEVICES FOR PREVENTING UNWANTED MOVEMENT OF VEHICLES; VEHICLE MODIFICATIONS TO FACILITATE COOLING OF BRAKES
    • B60T8/00—Arrangements for adjusting wheel-braking force to meet varying vehicular or ground-surface conditions, e.g. limiting or varying distribution of braking force
    • B60T8/32—Arrangements for adjusting wheel-braking force to meet varying vehicular or ground-surface conditions, e.g. limiting or varying distribution of braking force responsive to a speed condition, e.g. acceleration or deceleration
    • B60T8/34—Arrangements for adjusting wheel-braking force to meet varying vehicular or ground-surface conditions, e.g. limiting or varying distribution of braking force responsive to a speed condition, e.g. acceleration or deceleration having a fluid pressure regulator responsive to a speed condition
    • B60T8/40—Arrangements for adjusting wheel-braking force to meet varying vehicular or ground-surface conditions, e.g. limiting or varying distribution of braking force responsive to a speed condition, e.g. acceleration or deceleration having a fluid pressure regulator responsive to a speed condition comprising an additional fluid circuit including fluid pressurising means for modifying the pressure of the braking fluid, e.g. including wheel driven pumps for detecting a speed condition, or pumps which are controlled by means independent of the braking system
    • B60T8/4072—Systems in which a driver input signal is used as a control signal for the additional fluid circuit which is normally used for braking
    • B60T8/4081—Systems with stroke simulating devices for driver input
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B60—VEHICLES IN GENERAL
    • B60T—VEHICLE BRAKE CONTROL SYSTEMS OR PARTS THEREOF; BRAKE CONTROL SYSTEMS OR PARTS THEREOF, IN GENERAL; ARRANGEMENT OF BRAKING ELEMENTS ON VEHICLES IN GENERAL; PORTABLE DEVICES FOR PREVENTING UNWANTED MOVEMENT OF VEHICLES; VEHICLE MODIFICATIONS TO FACILITATE COOLING OF BRAKES
    • B60T8/00—Arrangements for adjusting wheel-braking force to meet varying vehicular or ground-surface conditions, e.g. limiting or varying distribution of braking force
    • B60T8/32—Arrangements for adjusting wheel-braking force to meet varying vehicular or ground-surface conditions, e.g. limiting or varying distribution of braking force responsive to a speed condition, e.g. acceleration or deceleration
    • B60T8/34—Arrangements for adjusting wheel-braking force to meet varying vehicular or ground-surface conditions, e.g. limiting or varying distribution of braking force responsive to a speed condition, e.g. acceleration or deceleration having a fluid pressure regulator responsive to a speed condition
    • B60T8/42—Arrangements for adjusting wheel-braking force to meet varying vehicular or ground-surface conditions, e.g. limiting or varying distribution of braking force responsive to a speed condition, e.g. acceleration or deceleration having a fluid pressure regulator responsive to a speed condition having expanding chambers for controlling pressure, i.e. closed systems
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B60—VEHICLES IN GENERAL
    • B60T—VEHICLE BRAKE CONTROL SYSTEMS OR PARTS THEREOF; BRAKE CONTROL SYSTEMS OR PARTS THEREOF, IN GENERAL; ARRANGEMENT OF BRAKING ELEMENTS ON VEHICLES IN GENERAL; PORTABLE DEVICES FOR PREVENTING UNWANTED MOVEMENT OF VEHICLES; VEHICLE MODIFICATIONS TO FACILITATE COOLING OF BRAKES
    • B60T2270/00—Further aspects of brake control systems not otherwise provided for
    • B60T2270/82—Brake-by-Wire, EHB

Definitions

  • the present invention relates to an automotive brake control system.
  • Brake control systems comprise a stroke simulator for generating force reacting to a driver's braking operation and use a hydraulic pressure source separate from a master cylinder to generate hydraulic pressure that is applied to the wheel cylinders at road wheels (e.g., Patent Document 1).
  • Patent Document 1 International Publication No. 2011/029812
  • the object of the present invention is to provide a brake control system with an improved response to a demand for increasing wheel cylinder pressure without the need for increasing an actuator in size, etc.
  • the brake control system of the present invention applies pressure to the wheel cylinders, preferably using brake fluid flowing from a stroke simulator that operates in response to the driver's brake operation.
  • FIG. 1 is a schematic view of a brake control system of a first embodiment.
  • FIG. 2 is a flowchart of the essential part of control of wheel cylinder hydraulic pressure of the first embodiment.
  • FIG. 3 is a time chart of the control of wheel cylinder hydraulic pressure of the first embodiment.
  • FIG. 4 is a schematic view of a brake control system of a second embodiment.
  • FIG. 5 is an enlarged schematic view of second to fourth hydraulic lines 12 to 14 of the second embodiment (in a non-emergency brake operation).
  • FIG. 6 is an enlarged schematic view of the second to fourth hydraulic lines 12 to 14 of the second embodiment (in an emergency brake operation).
  • FIG. 7 is a schematic view of a brake control system of a third embodiment.
  • FIG. 8 is a schematic view of a brake control system of a fourth embodiment.
  • FIG. 9 is a flowchart of the essential part of wheel cylinder hydraulic pressure control of the fourth embodiment.
  • FIG. 10 is a time chart of the wheel cylinder hydraulic pressure control of the fourth embodiment (in a non-emergency operation).
  • FIG. 11 is a time chart of the wheel cylinder hydraulic pressure control of the fourth embodiment (in an emergency operation).
  • FIG. 12 is a schematic view of a brake control system of a fifth embodiment.
  • FIG. 13 is a schematic view of a brake control system of a sixth embodiment.
  • FIG. 14 is a flowchart of the essential part of wheel cylinder hydraulic pressure control of the sixth embodiment.
  • FIG. 15 is a time chart of the wheel cylinder hydraulic pressure control of the sixth embodiment (in a non-emergency operation).
  • FIG. 16 is a time chart of the wheel cylinder hydraulic pressure control of the sixth embodiment (in an emergency operation).
  • FIG. 1 schematically shows the structure of system 1 .
  • System 1 is a hydraulic brake system suited for a hybrid vehicle equipped with a motor generator (electric motor) as a drive for driving the wheels, in addition to an engine (internal combustion engine), and an electrically powered vehicle, such as one that solely relies on a motor generator.
  • System 1 may also be applied to a vehicle that solely relies on an engine for drive power.
  • System 1 supplies wheel cylinders 8 at wheels FL to RR of the vehicle with brake fluid to generate brake fluid pressure (wheel cylinder hydraulic pressure) that acts as hydraulic braking force on wheels FL to RR.
  • Wheel cylinders 8 may be ones of a hydraulic brake caliper of a disk brake mechanism as well as a drum brake mechanism.
  • System 1 comprises two brake piping systems (P (primary) system and S (secondary system)) of, for example, a diagonally split configuration.
  • the brake piping systems may, instead, be of other configuration, such as a front-rear split configuration.
  • the members of the P system are indicated by the letter P and the S system by S to distinguish them, where necessary.
  • Brake pedal 2 is a brake operation member that receives an input from a driver through brake operation. Brake pedal 2 is provided with stroke sensor 90 for sensing the displacement of brake pedal 2 .
  • the displacement of brake pedal 2 is a brake stroke representing the amount of the driver's brake operation.
  • Stroke sensor 90 may, instead, sense the displacement of a piston (e.g., primary piston 52 P, which will be described later) of master cylinder 5 as a pedal stroke.
  • Brake pedal 2 is pivotally connected at its root to an end of pushrod 30 .
  • Reservoir tank (reservoir) 4 is a brake fluid source, which is a low pressure section exposed to the atmospheric pressure.
  • Master cylinder 5 generates brake hydraulic pressure (master cylinder pressure) in response to the driver's operation of brake pedal 2 (brake operation).
  • Master cylinder 5 is connected via pushrod 30 to brake pedal 2 and is supplied with brake fluid from reservoir tank 4 .
  • Master cylinder 5 is of tandem type comprising master cylinder pistons that move axially in response to the driver's brake operation, namely, primary piston 52 P connected to pushrod 30 and second piston 52 S of free piston type.
  • system 1 does not have a vacuum booster that uses intake negative pressure generated by the vehicle engine to boost the brake operation (pedal effort).
  • System 1 comprises hydraulic pressure control unit 6 and electronic control unit 100 .
  • Hydraulic pressure control unit 6 is a brake control unit that operates, independent of the driver's brake operation, to generate hydraulic pressure by receiving a supply of brake fluid from reservoir tank 4 or master cylinder 5 .
  • Electronic control unit (ECU) 100 is a control unit for controlling the operation of hydraulic pressure control unit 6 .
  • Hydraulic pressure control unit 6 is located between wheel cylinders 8 and master cylinder 5 to individually supply wheel cylinders 8 with master cylinder hydraulic pressure or control hydraulic pressure.
  • Hydraulic pressure control unit 6 has motor 7 a of pump 7 and a plurality of control valves (solenoid valves 21 or the like) serving as a hydraulic pressure device (actuator) for generating control hydraulic pressure.
  • Pump 7 takes brake fluid from reservoir tank 4 while electric motor 7 a (electric motor) is running and delivers the brake fluid to wheel cylinders 8 .
  • pump 7 is a gear pump having excellent noise/judder characteristics or the like, namely, an external gear pump unit. Pump 7 is shared by the two systems and driven by single motor 7 a serving as a drive source.
  • Motor 7 a may be, for example, a brush motor. Motor 7 a is provided with a resolver for sensing the rotational position (angle of rotation) of the output shaft of motor 7 . Solenoid valves 21 or the like open and close in response to a control signal to control a flow of brake fluid. With communication between master cylinder 5 and wheel cylinders 8 cut off, hydraulic pressure control unit 6 uses hydraulic pressure generated by pump 7 to increase the pressure in wheel cylinders 8 . Hydraulic pressure control unit 6 comprises stroke simulator 22 . Stroke simulator 22 operates in accordance with the driver's brake operation to receive brake fluid transmitted from master cylinder 5 to generate a pedal stroke. Hydraulic pressure control unit 6 comprises hydraulic sensors 91 to 93 that sense hydraulic pressures at different locations, such as the output pressure from pump 7 and master cylinder pressure.
  • ECU 100 receives sensor values from the resolver, pedal stroke sensor 90 and hydraulic sensors 91 to 93 and information on driving conditions sent from the vehicle. Using these items of information, ECU 100 performs information processing, following a stored program. On the basis of the result of this processing, ECU 100 outputs a control command to each actuator of hydraulic pressure control unit 6 to control the actuators. More specifically, ECU 100 controls opening/closing operation of solenoid valves 21 or the like, which change the state of communication of hydraulic line 11 or the like, and also controls the rotational speed (the amount of fluid from pump 7 ) of motor 7 a for driving pump 7 .
  • ECU 100 achieves boost control that assists in braking operation by generating hydraulic braking force to compensate for any shortage of the driver's braking effort, antilock control for minimizing slip (lockup tendency) of wheels FL to RR caused by braking, brake control for vehicle dynamic control (vehicle stability control for antiskid, etc.; hereinafter “ESC”), automatic braking control, such as adaptive cruise control, cooperative regenerative braking control for controlling the hydraulic pressure in the wheel cylinders to attain a target deceleration (target braking force) in cooperation with regenerative braking or such other control.
  • boost control that assists in braking operation by generating hydraulic braking force to compensate for any shortage of the driver's braking effort
  • antilock control for minimizing slip (lockup tendency) of wheels FL to RR caused by braking
  • brake control for vehicle dynamic control vehicle dynamic control
  • ESC vehicle stability control for antiskid, etc.
  • automatic braking control such as adaptive cruise control, cooperative regenerative braking control for controlling the hydraulic pressure in the wheel cylinders to attain
  • Master cylinder 5 is connected via first hydraulic line 11 (described later) to wheel cylinders 8 and serves as a first hydraulic pressure source for increasing wheel cylinder hydraulic pressure.
  • Master cylinder 5 uses master cylinder pressure generated in first fluid chamber (primary chamber) 51 P to apply pressure to wheel cylinders 8 a and 8 d via a hydraulic line (first hydraulic line 11 P) of system P, and also uses master cylinder pressure generated in second fluid chamber (secondary chamber) 51 S to apply pressure to wheel cylinders 8 b and 8 c via a hydraulic line (first hydraulic line 11 S) of system S.
  • Pistons 52 of master cylinder 5 are inserted in a tubular cylinder 50 having a closed bottom to move axially along the inner circumferential surface of cylinder 50 .
  • Cylinder 50 comprises outlet port (supply port) 501 and inlet port 502 both for each of systems P and S.
  • Outlet port 501 is connected to hydraulic pressure control unit 6 to communicate with wheel cylinders 8 .
  • Inlet port 502 is communicatively connected to reservoir tank 4 .
  • First fluid chamber 51 P located between pistons 52 P and 52 S, contains compressed coil spring 53 P, serving as a return spring.
  • Second fluid chamber 51 S located between piston 52 S and the axial end of cylinder 50 , contains compressed coil spring 53 S.
  • Each of first and second fluid chambers 51 P and 51 S has outlet port 501 normally open thereto.
  • Cylinder 50 has piston seals 54 (at numerals 541 and 542 in the figure) on the inner circumference thereof.
  • Piston seals 54 are a plurality of seal members that slide on seal piston 52 P or 52 S to seal between the outer circumferential surface of each of pistons 52 P and 52 S and the inner circumferential surface of cylinder 50 .
  • Each piston seal 54 is a seal member (cup seal) of a known cup-shaped cross section having a lip on its inner radial side. When the lip is in contact with the outer circumferential surface of piston 52 , brake fluid is allowed to flow in one direction and is prevented from flowing in the other direction.
  • First piston seal 541 allows brake fluid to flow from inlet port 502 toward first and second fluid chambers 51 P and 51 S (outlet port 501 ), while preventing brake fluid from flowing in the opposite direction.
  • Second piston seal 542 allows brake fluid to flow toward inlet port 502 , while preventing fluid brake from flowing out from inlet port 502 .
  • First and second fluid chambers 51 P and 51 S decrease in volume to develop hydraulic pressure (master cylinder pressure) as pistons 52 are moved in the axial direction opposite to brake pedal 2 by the driver stepping on brake pedal 2 . This causes brake fluid to pass from first and second fluid chambers 51 P and 51 S through outlet ports 501 to wheel cylinders 8 .
  • Systems P and S generate substantially equal levels of hydraulic pressure in first and second fluid chambers 51 P and 51 S.
  • Hydraulic line 11 connects outlet ports 501 (first and second fluid chambers 51 P and 51 S) of master cylinder 5 to wheel cylinders 8 .
  • Cutoff valve 21 is a normally open solenoid valve (that is open when electric current is not applied thereto) in first hydraulic line 11 .
  • First hydraulic line 11 is divided by cutoff valve 21 into hydraulic line 11 A on the master cylinder 5 side and hydraulic line 11 B on the wheel cylinder 8 side.
  • Solenoid IN valves (pressure increasing valves) SOL/V IN 25 are normally open solenoid valves on respective wheels FL to RR (or in respective hydraulic lines 11 a to 11 d ) on the wheel cylinder 8 side (hydraulic line 8 side) of cutoff valve 21 in first hydraulic line 11 . Disposed in parallel to first hydraulic line 11 is bypass hydraulic line 110 that bypasses SOL/V IN 25 . Bypass hydraulic line 110 is provided with a check valve (one-way valve) 250 that admits only brake fluid flowing from the wheel cylinder 8 side to the master cylinder 5 side.
  • Inlet hydraulic line 15 connects reservoir tank 4 to inlet 70 of pump 7 .
  • Outlet hydraulic line 16 connects outlet 71 of pump 7 to a portion of first hydraulic line 11 connecting cutoff valve 21 to SOL/V IN 25 .
  • Check valve 160 is an outlet valve of pump 7 that is located in outlet hydraulic line 16 and admits only brake fluid flowing from the outlet 71 side to the first hydraulic line 11 side.
  • Outlet hydraulic line 16 divides at point P 1 on the downstream side of check valve 160 into outlet hydraulic line 16 P of system P and outlet hydraulic line 16 S of system S.
  • Hydraulic lines 16 P and 16 S are connected to first hydraulic line 11 P of system P and first hydraulic line 11 S of system S, respectively.
  • Outlet hydraulic lines 16 P and 16 S form a communication passage interconnecting first hydraulic lines 11 P and 11 S.
  • Communication valve 26 P is a normally closed solenoid valve (closed when electric current is not applied) provided in outlet hydraulic line 16 P.
  • Communication valve 26 S is a normally closed solenoid valve provided in outlet hydraulic line 16 S.
  • Pump 7 is a second hydraulic pressure source that uses brake fluid supplied from reservoir tank 4 to generate hydraulic pressure in first hydraulic line 11 . Pump 7 is connected via the communication passage (outlet hydraulic lines 16 P and 16 S) and first hydraulic lines 11 P and 11 S to wheel cylinders 8 a to 8 d and can increase wheel cylinder hydraulic pressure by delivering brake fluid to the communication passage (outlet hydraulic lines 16 P and 16 S).
  • First pressure-reducing hydraulic line 17 connects inlet hydraulic line 15 to a portion of outlet hydraulic line 16 between check valve 160 and communication valve 26 .
  • first pressure reducing hydraulic line 17 connects point P 1 and point P 2 .
  • Pressure regulating valve 27 is a normally open solenoid valve serving as a first pressure reducing valve in first pressure reducing hydraulic line 17 .
  • Second pressure reducing hydraulic line 18 connects inlet hydraulic line 15 to a portion of first hydraulic line 11 (hydraulic line 11 B) on the wheel cylinder 8 side of SOL/V IN 25 .
  • second pressure reducing hydraulic line 18 connects point P 3 and point P 4 .
  • Solenoid OUT valve (pressure reducing valve) SOL/V OUT 28 is a normally closed solenoid valve serving as a second pressure reducing valve in second pressure reducing line 18 .
  • Second hydraulic line 12 is a branch hydraulic line that branches at point P 5 off from first hydraulic line 11 P and connects to stroke simulator 22 .
  • Stroke simulator 22 comprises piston 220 and spring 221 .
  • Piston 200 is a partition wall that divides the interior of cylinder 22 a of stroke simulator 22 into two chambers (positive pressure chamber R 1 and backpressure chamber R 2 ), and is axially movable in cylinder 22 a .
  • the word “axially” refers to the direction of compression of spring 221 .
  • Piston 220 has a seal member (not shown) on its outer circumferential surface, facing the inner circumferential surface of cylinder 22 a .
  • the seal member seals off the outer circumference of the piston 220 to prevent communication of brake fluid between the positive pressure chamber (primary chamber) R 1 and the backpressure chamber (secondary chamber) R 2 , thereby keeping chambers R 1 and R 2 fluid-tight against each other.
  • Spring 221 is a coil spring (elastic member) compressed in backpressure chamber R 2 , namely, urging means that always urge piston 200 toward the positive pressure chamber R 1 (in the direction of reducing the volume of positive pressure chamber R 1 and increasing the volume of backpressure chamber R 2 ).
  • Spring 221 is so disposed as to exert reaction force according to a displacement (stroke) of piston 220 .
  • Second hydraulic line 12 branches off at point 5 from a portion (hydraulic line 11 A) of first hydraulic line 11 P between outlet port 50 P (first fluid chamber 51 P) of master cylinder 5 and cutoff valve 21 P and connects to positive-pressure chamber R 1 of stroke simulator 22 .
  • Third hydraulic line 13 is a first back-pressure hydraulic line connecting backpressure chamber R 2 of stroke simulator 22 to first hydraulic line 11 .
  • Third hydraulic line 13 branches off at position P 6 between cutoff valve 21 P and SOL/V IN 25 in first hydraulic line 11 P (hydraulic line 11 B) and connects to backpressure chamber R 2 of stroke simulator 22 .
  • Stroke simulator IN valve SS/V IN 23 is a normally closed first simulator cutoff valve in third hydraulic line 13 .
  • Third hydraulic line 13 is divided by SS/V IN 23 into hydraulic line 13 A on the backpressure chamber R 2 side and hydraulic line 13 B on the first hydraulic line 11 side.
  • Fourth hydraulic line 14 is a second backpressure hydraulic line connecting backpressure chamber R 2 of stroke simulator 22 and reservoir tank 4 .
  • Fourth hydraulic line 14 connects hydraulic line 13 A of third hydraulic line 13 , located between backpressure chamber R 2 and SS/V IN 23 , and inlet hydraulic line 15 .
  • Stroke-simulator OUT valve SS/V OUT 24 is a normally closed second simulator cutoff valve in fourth hydraulic line 14 .
  • fourth hydraulic line 14 may be directly connected to backpressure chamber R 2 or reservoir tank 4 .
  • part of fourth hydraulic line 14 on the backpressure chamber R 2 side corresponds to third hydraulic line 13
  • part of fourth hydraulic line 14 on the reservoir tank 4 side corresponds to part of inlet hydraulic line 15 , so as to simplify the overall hydraulic line structure.
  • third hydraulic line 13 can be thought of as connecting hydraulic line 11 B and the portion of fourth hydraulic line 14 between backpressure chamber R 2 and SS/V OUT 24 .
  • hydraulic line 13 A forms part of fourth hydraulic line 14
  • third hydraulic line 13 consists only of hydraulic line 13 B.
  • Cutoff valve 21 , SOL/V IN 25 , and pressure regulating valve 27 are proportional control valves that adjust the degree of valve opening in accordance with electric current applied to their solenoid.
  • the other valves namely, communication valve 26 , SOL/V OUT valve 28 , SS/V OUT 24 , and SS/V IN 23 are on-off valves that are controlled to switch between two values to open and close. These other valves may instead be proportional control valves.
  • hydraulic sensor 91 In a portion (hydraulic line 11 A) of first hydraulic line 11 P between cutoff valve 21 P and master cylinder 5 is disposed hydraulic sensor 91 for sensing hydraulic pressure in that portion (master cylinder pressure and hydraulic pressure in positive pressure chamber R 1 of stroke simulator 22 ).
  • Hydraulic sensor 91 may instead be disposed in second hydraulic line 12 .
  • a hydraulic sensor primary-system pressure sensor, secondary-system pressure sensor
  • 92 for sensing hydraulic pressure (wheel cylinder hydraulic pressure) in that portion.
  • hydraulic sensor 93 for sensing hydraulic pressure (pump outlet pressure) in that portion.
  • Hydraulic sensor 93 may instead be disposed in a portion of outlet hydraulic line 16 between outlet 71 (check valve 160 ) of pump 7 and communication valve 26 .
  • Hydraulic pressure control unit 6 comprises first unit 61 and second unit 62 .
  • First unit 61 comprises cutoff valve 21 P of system P, SS/V IN 23 , SS/V OUT 24 , and hydraulic sensor 91 , in addition to stroke simulator 22 .
  • Second unit 62 comprises the other actuators and sensors in addition to pump 7 , namely, valves 21 S and 25 to 28 , hydraulic sensors 92 and 93 , and motor 7 a .
  • Second unit 62 is integrated with ECU 100 .
  • First unit 61 is integrated with the unit comprising master cylinder 5 and reservoir tank 4 . In other words, master cylinder 5 and stroke simulator 22 are housed in separate housings.
  • First unit 61 containing stroke simulator 22 , is integrated with master cylinder 5 , such that first unit 61 and master cylinder 5 together form one unit.
  • Pump 7 is housed in a housing separate from master cylinder 5 and stroke simulator 22 .
  • Pump 7 and valves 21 S and 25 to 28 are housed in the same housing to form a hydraulic unit (second unit 62 ).
  • First and second units 61 and 62 are adapted to actively control the master cylinder hydraulic pressure and the wheel cylinder hydraulic pressure by controlling the actuators in response to a control command from ECU 100 .
  • the brake system (first hydraulic line 11 ) connecting fluid chamber 51 of master cylinder 5 and wheel cylinders 8 forms a first system that uses master cylinder pressure exerted by pedal effort to generate wheel cylinder hydraulic pressure and thereby achieves pedal effort braking (control without boosting).
  • the brake system (inlet hydraulic line 15 , outlet hydraulic line 16 , etc.) including pump 7 and connecting reservoir tank 4 and wheel cylinders 8 forms a second system that uses hydraulic pressure generated by pump 7 to generate wheel cylinder hydraulic pressure, that is, a so-called brake-by-wire system that achieves boost control or the like.
  • stroke simulator 22 During brake-by-wire control, stroke simulator 22 generates reaction force in response to the driver's braking operation. With cutoff valve 21 closed and the communication between master cylinder 5 and wheel cylinders 8 cut off, stroke simulator 22 generates a pedal stroke by allowing at least brake fluid coming out of master cylinder 5 (first fluid chamber 51 P) to first hydraulic line 11 P to flow via second hydraulic line 12 into positive pressure chamber R 1 . With SS/V OUT 24 open establishing communication between backpressure chamber R 2 and reservoir tank 4 , stroke simulator 22 generates a pedal stroke in such a manner that positive pressure chamber R 1 allows brake fluid to flow into or out of master cylinder 5 as the driver performs braking operation (stepping on brake pedal 2 or releasing it).
  • Fourth hydraulic line 14 serves its purpose as long as it is connected to a low-pressure section into which brake fluid can flow, and is not required to be connected to reservoir tank 4 .
  • the urging force (resilient force) of spring 221 returns piston 220 to its initial position. Since the reaction force exerted by spring 221 acting on piston 220 is proportional to the displacement of piston 220 , reaction force generated that acts on brake pedal 2 (hereinafter “pedal reaction force”) is proportional to the operation of brake pedal 2 . Drawing brake fluid from master cylinder 5 and generating the pedal reaction force in this manner, stroke simulator 22 reproduces a proper feel of the pedal when depressed, approximating the stiffness of fluid in wheel cylinders 8 .
  • ECU 100 comprises: brake operating condition detector 101 ; calculator 102 for calculating a target wheel cylinder hydraulic pressure; pedal-effort braking force generator 103 ; and wheel-cylinder hydraulic pressure controller 104 .
  • Brake operating condition detector 101 receives an input of a value sensed by stroke sensor 90 , thereby measuring a displacement (pedal stroke S) of brake pedal 2 as an amount of brake operation. More specifically, brake operating condition detector 101 receives a value output from stroke sensor 90 and calculates pedal stroke S.
  • Brake operating condition detector 101 determines whether the driver is operating the brakes (whether brake pedal 2 is being operated) on the basis of pedal stroke S and measures or estimates the rate of driver's brake operation.
  • the rate of brake operation is measured or estimated by computing the rate of change of pedal stroke S (pedal stroke speed ⁇ S/ ⁇ t).
  • Stroke sensor 90 is not limited to one that directly senses a displacement of brake pedal 2 , and may be one that senses a displacement of pushrod 3 .
  • a pedal sensor for sensing force acting on brake pedal 2 may be used to measure or estimate an amount of brake operation from a value sensed by the pedal sensor.
  • the amount of brake operation may instead be measured or estimated on the basis of a value sensed by hydraulic sensor 91 .
  • the amount of brake operation used for control is not limited to the pedal stroke and may be any other proper variable.
  • Calculator 102 for calculating a target wheel-cylinder hydraulic pressure calculates a target wheel-cylinder hydraulic pressure. For example, during boost control, calculator 102 for calculating a target wheel-cylinder hydraulic pressure calculates, on the basis of a pedal stroke detected, target wheel-cylinder hydraulic pressure Pw* that achieves ideal characteristics of the relation between the pedal stroke and a brake hydraulic pressure required by the driver (vehicle deceleration G required by the driver), in accordance with a predetermined boost ratio.
  • this embodiment uses predetermined characteristics of the relation between a pedal stroke and a wheel-cylinder hydraulic pressure (braking force) achieved during operation of the vacuum booster as the above-described ideal relational characteristics for calculating target wheel-cylinder hydraulic pressure Pw*.
  • calculator 102 for calculating a target wheel-cylinder hydraulic pressure calculates target wheel-cylinder hydraulic pressure Pw* for each of wheels FL to RR to bring the wheel to a proper degree of slip (amount of deviation of the speed of the wheel from a simulated vehicle speed).
  • calculator 102 for calculating a target wheel-cylinder hydraulic pressure calculates target wheel-cylinder hydraulic pressure Pw* for each of wheels FL to RR on the basis of, for example, a measured amount of vehicle dynamic conditions (e.g., lateral acceleration) to achieve desired vehicle dynamic conditions.
  • calculator 102 for calculating a target wheel-cylinder hydraulic pressure calculates target wheel-cylinder hydraulic pressure Pw* in relation to regenerative braking force.
  • target wheel-cylinder hydraulic pressure Pw* so calculated is such that the sum of a regenerative braking force input from a control unit of a regenerative braking system and a hydraulic braking force corresponding to the target wheel-wheel hydraulic pressure satisfies a vehicle deceleration required by the driver.
  • Pedal-effort braking force generator 103 opens cutoff valve 21 and thereby brings hydraulic pressure control unit 6 into a condition of generating wheel cylinder hydraulic pressure from master cylinder pressure (first system) to achieve pedal-effort braking.
  • master cylinder pressure first system
  • SS/V OUT 24 and SS/V IN 23 are closed so that stroke simulator 22 does not respond to the driver's brake operation.
  • SS/V IN 23 may be opened.
  • Wheel-cylinder hydraulic pressure controller 104 closes cutoff valve 21 and thereby brings hydraulic pressure control unit 6 into a condition in which pump 7 (second system) can be used to generate wheel cylinder hydraulic pressure (pressure-increasing control), so as to perform hydraulic control (e.g., boost control) that achieves a target wheel-cylinder hydraulic pressure by controlling the actuators of hydraulic pressure control unit 6 . More specifically, wheel-cylinder hydraulic pressure controller 104 closes cutoff valve 21 , opens communication valve 26 , closes pressure-regulating valve 27 , and actuates pump 7 . This control enables a desired amount of brake fluid to flow from reservoir tank 4 via inlet hydraulic line 15 , pump 7 , outlet line 16 , and first hydraulic line 11 into wheel cylinders 8 .
  • hydraulic control e.g., boost control
  • the rotational speed of pump 7 and the opening (e.g., degree of opening) of pressure-regulating valve 27 are controlled by feedback to bring a value sensed by hydraulic sensor 92 toward a target wheel-cylinder hydraulic pressure, thereby providing a desired braking force.
  • the opening of pressure-regulating valve 27 is controlled to allow brake fluid to escape from outlet hydraulic line 16 or first hydraulic line 11 through pressure-regulating valve 27 into inlet hydraulic line 15 , as required, thereby making it possible to adjust wheel cylinder pressure.
  • This control of pressure-regulating valve 27 is hereinafter referred to as escape control.
  • the degree of opening of pressure-regulating valve 27 is adjusted (escape control) to control wheel-cylinder hydraulic pressure.
  • a command value for the rotational speed of motor 7 a is set to a large value fixed while increasing wheel cylinder hydraulic pressure, and is otherwise held at a small fixed value while holding or decreasing the wheel cylinder hydraulic pressure, so as to generate a required minimum pump discharge pressure (provide a pump discharge rate). Since this embodiment uses a proportional control valve for pressure-regulating valve 27 , fine control can be performed to achieve smooth control of the wheel cylinder hydraulic pressure.
  • Cutoff valve 21 can be closed to cut the master cylinder 5 side off from the wheel cylinder 8 side to facilitate control of the wheel cylinder hydraulic pressure independent of the driver's pedal operation.
  • wheel-cylinder hydraulic pressure controller 104 performs boost control.
  • boost control SOL/V IN 25 on each of wheels FL to RR is opened, and SOL/V OUT 28 is closed.
  • cutoff valves 21 P and 21 S are closed, pressure regulating valve 27 is closed (under feedback control of the degree of opening or the like) and communication valve 26 is opened, and pump 7 is actuated with rotational speed command valve Nm* for motor 7 a set to a fixed value.
  • SS/V OUT 24 is opened and SS/V IN 23 is closed.
  • Wheel-cylinder hydraulic pressure controller 104 has auxiliary pressure controller 105 .
  • Auxiliary pressure control supplements the wheel cylinder pressure generated from pump 7 by supplying brake fluid flowing from backpressure chamber R 2 of stroke simulator 22 to wheel cylinders 8 during the driver's brake control.
  • the auxiliary pressure control serves as a backup control for the wheel cylinder pressure control by pump 7 .
  • Auxiliary pressure controller 105 executes the auxiliary pressure control in accordance with the driver's braking operation when wheel-cylinder hydraulic pressure control 104 increases the wheel cylinder hydraulic pressure at wheels FL to RR in accordance with the driver's operation of brake pedal 2 (an increase in pedal stroke) (when controlling the pressure on the wheel cylinders with the aid of pump 7 ) during normal brake operation (boost control).
  • SS/V OUT 24 is closed and SS/V IN 23 is opened.
  • the path of brake fluid flowing from backpressure chamber R 2 of stroke simulator 22 in response to the driver's brake operation which path has led through fourth hydraulic line 14 to reservoir tank 4 , now serves as a flow path that leads through third hydraulic line 13 to first hydraulic line 11 P ( 11 B).
  • the brake fluid flowing from backpressure chamber R 2 in response to the driver's pedal effort is now sent through third hydraulic line 13 to first hydraulic line 11 P ( 11 B).
  • This brake fluid acts to pressurize wheel cylinders 8 to supplement the hydraulic pressure on wheel cylinders 8 exerted by pump 7 .
  • SS/V OUT 24 and SS/V IN 23 serve as a switch for switching the flow path.
  • Auxiliary pressure controller 105 determines whether the driver's brake operation is a predetermined emergency braking operation or not. If yes (if brake pedal 2 is stepped on rapidly), auxiliary pressure controller 105 performs auxiliary pressure control. If no (if brake pedal 2 is not stepped on rapidly), it does not perform auxiliary pressure control. If the brake operating rate measured or estimated by brake operating condition detector 101 is greater than or equal to a set value, auxiliary pressure controller 105 recognizes the braking operation as the above-mentioned predetermined emergency brake operation. If the brake operating rate is lower than the set value, it recognizes the braking operation as non-emergency.
  • auxiliary pressure control is performed if a measured or estimated rotational speed Nm of motor 7 a is a set value Nm 0 or less and a measured pedal stroke S (amount of braking is less than or equal to a set value S 0 ).
  • FIG. 2 is a flowchart of the control by wheel cylinder hydraulic pressure controller 104 during normal braking (boost control). This process is programmed as software in ECU 100 and is repeated at predetermined intervals.
  • step S 1 auxiliary pressure controller 105 determines whether the braking rate (pedal stroke speed ⁇ S/ ⁇ t) measured or estimated by brake operating condition detector 101 is greater than or equal to a set value ⁇ . If yes, it recognizes the braking operation as an emergency one, and the process goes to step S 2 . If no, it recognizes the braking operation as a non-emergency one, and the process goes to step S 4 .
  • auxiliary pressure controller 105 determines whether the rotational speed of motor 7 a detected or estimated from a detection signal from a resolver (hereinafter “motor rotational speed Nm”) is less than or equal to a set value Nm 0 (a final determining threshold for auxiliary pressure control) and pedal stroke S sensed by brake operating condition detector 101 is a set value S 0 (a final determining threshold for auxiliary pressure control) or less. If motor rotational speed Nm is a set value Nm 0 or less and pedal stroke S is a set value S 0 or less, the process goes to step S 3 . If motor rotational speed Nm is greater than set value Nm 0 or pedal stroke S is greater than set value S 0 , the process goes to step S 4 .
  • step S 3 auxiliary pressure controller 105 activates (opens) SS/V IN 23 and deactivates (closes) SS/V OUT 24 and implements auxiliary pressure control.
  • step S 4 wheel cylinder hydraulic pressure controller 104 deactivates (closes) SS/V IN 23 and activates (opens) SS/V OUT 24 and does not implements (terminates) the auxiliary pressure control. In this manner, normal boost control is carried out.
  • Wheel cylinder hydraulic pressure controller 104 closes cutoff valve 21 when the driver steps on brake pedal 2 . This allows an amount of brake fluid flowing from master cylinder 5 (first fluid chamber 51 P), which amount corresponds to the pedal stroke, to flow via second hydraulic line 12 into positive pressure chamber R 1 of stroke simulator 22 .
  • first fluid chamber 51 P first fluid chamber 51 P
  • second hydraulic line 12 into positive pressure chamber R 1 of stroke simulator 22 .
  • piston 220 runs a stroke while compressing spring 221 . This allows the amount of brake fluid equivalent to the amount flowing into positive pressure chamber R 1 (corresponding to the pedal stroke) to flow from backpressure chamber R 2 .
  • SS/V OUT 24 is closed and SS/V IN 23 is opened.
  • brake fluid from backpressure chamber R 2 of stroke simulator 22 operated by the driver's pedal effort supplied via third hydraulic line 13 into first hydraulic line 11 P ( 11 B), exerts pressure on wheel cylinders 8 .
  • the force against piston 220 exerted by spring 221 and backpressure creates pedal reaction force.
  • FIG. 3 is a time chart of the operation of system 1 in the driver's emergency brake operation.
  • the driver does not perform brake operation, thus, there is no pedal stroke.
  • Wheel-cylinder hydraulic pressure controller 104 does not perform hydraulic pressure control; thus, master cylinder hydraulic pressure Pm, wheel cylinder hydraulic pressure Pw, motor rotational speed Nm are all zero. Since brake operating condition detector 101 detects non-braking operation, wheel-cylinder hydraulic pressure controller 104 closes SS/V OUT 24 and SS/V IN 23 and puts stroke simulator 22 inactive.
  • the driver starts brake operation and continues to step on brake pedal 2 until time t 5 . From t 1 , pedal stroke S rises from zero.
  • step S 1 to S 4 pedal stroke speed ⁇ S/ ⁇ t is less than set value ⁇ (threshold for emergency braking); thus, the process in the flowchart of FIG. 2 proceeds from step S 1 to S 4 , and wheel-cylinder hydraulic pressure controller 104 performs normal wheel cylinder pressure control. That is, command value Nm* for the rotational speed of motor 7 a is set to a large fixed value. Cutoff valve 21 is closed and SS/V IN 23 is closed and SS/V OUT 24 is opened. Due to a delay in control of motor 7 a (response delay), the actual value Nm has not reached the command value Nm* for motor rotational speed, the actual value Nm of motor rotational speed has not risen and remains zero. In this state, pump 7 is not in operation and wheel cylinder fluid pressure Pw hardly rises.
  • pedal stroke speed ⁇ S/ ⁇ t exceeds ⁇ .
  • Pedal stroke S is less than or equal to S 0 and motor rotational speed Nm (actual value) is Nm 0 or less; thus, the process goes from step S 1 to S 2 and to S 3 and auxiliary pressure controller 105 performs auxiliary pressure control.
  • command value Nm* for motor rotational speed at the fixed value and cutoff valve 21 closed, SS/V IN 23 is opened and SS/V OUT 24 is closed. This causes the amount of brake fluid, corresponding to pedal stroke S, flowing from backpressure chamber R 2 of stroke simulator 22 in response to the driver's braking operation, to flow via third hydraulic line 13 into first hydraulic line 11 P. This flow puts pressure on wheel cylinders 8 .
  • Wheel cylinder hydraulic pressure Pw represents the difference between master cylinder hydraulic pressure Pm and the hydraulic pressure corresponding to the urging force of the spring 221 (pedal reaction force during normal control) and increases with increasing master cylinder hydraulic pressure Pm.
  • actual value Nm of rotational speed of motor 7 a begins to rise from zero.
  • step S 4 pedal stroke S exceeds S 0 , or motor rotational speed Nm (actual value) exceeds Nm 0 .
  • the process thus goes from step S 1 to S 2 and to S 4 , and wheel-cylinder hydraulic pressure controller 104 again performs normal wheel cylinder pressure control. Since actual value Nm of motor rotational speed is greater than Nm 0 , the amount of brake fluid pumped by pump 7 becomes sufficient to add pressure to wheel cylinders 8 .
  • Wheel cylinder hydraulic pressure Pw is brought up to a value greater than master cylinder hydraulic pressure Pm (boost control) and rises steeply than master cylinder hydraulic pressure Pm.
  • wheel-cylinder hydraulic pressure controller 104 controls hydraulic pressure control unit 6 to hold wheel cylinder hydraulic pressure Pw.
  • Command value Nm* of motor rotational speed is lowered compared with that during the increase of wheel cylinder hydraulic pressure Pw (wheel cylinder pressure control) and is held at a low set value.
  • the driver releases brake pedal 2 , causing pedal stroke S to decrease up to t 7 .
  • wheel-cylinder hydraulic pressure controller 104 controls hydraulic pressure control unit 6 to reduce wheel cylinder hydraulic pressure Pw.
  • Command value Nm* of motor rotational speed is held to the low set value.
  • pedal stroke S reaches zero, putting the brake operation to an end.
  • Wheel-cylinder hydraulic pressure controller 104 thus ends the hydraulic pressure control.
  • command value Nm* of motor rotational speed is set to zero and SS/V OUT 24 and SS/V IN 23 are closed.
  • rotational speed Nm of motor 7 a (the performance of pump 7 a to supply) is not sufficient to generate wheel cylinder hydraulic pressure Pw for an emergency brake operation, although pump 7 (motor 7 a ) is running, and pedal stroke S is small (the amount of brake fluid required for wheel cylinder pressurization is large while required force is small).
  • the wheel cylinder pressure control with the aid of pump 7 is augmented by auxiliary pressure control utilizing the force on brake pedal 2 .
  • rotational speed Nm of motor 7 a (the performance of pump 7 to supply) becomes sufficiently large or pedal stroke S increases (force required for wheel cylinder pressurization is large while the amount of braked fluid required is small).
  • pedal stroke S exceeds set value S 0 at the time (time t 4 ) when motor rotational speed Nm exceeds set value Nm 0 ; however, there may be a time lag between these two events.
  • Wheel-cylinder hydraulic pressure controller 104 has antilock controller 106 .
  • Antilock controller 106 reads the speed of each of wheels FL to RR as vehicle information and detects and monitors the slip condition of wheels FL to RR.
  • wheel-cylinder hydraulic pressure controller 104 intervenes in hydraulic control (boost control) for brake operation and increases or decreases the hydraulic pressure in the wheel cylinder 8 at the wheel with an excessive degree of slip, with cutoff valve 21 closed. This control brings the degree of slip of that wheel to a proper value.
  • a hydraulic pressure command for the wheel cylinder 8 is to reduce the hydraulic pressure, SOL/V IN 25 on that wheel cylinder 8 is closed, and SOL/V OUT 28 is opened, so as to bring brake fluid in the wheel cylinder 8 into inlet hydraulic line 15 for pressure decrease. If a hydraulic-pressure command for the wheel cylinder 8 is to hold the hydraulic pressure, SOL/V OUT 28 and SOL/V IN 25 on the wheel cylinder 8 are closed, thereby holding the hydraulic pressure in the wheel cylinder 8 .
  • Wheel-cylinder hydraulic pressure controller 104 controls stroke simulator 22 by regulating the operation of SS/V IN 23 and SS/V OUT 24 in accordance with the operating condition of antilock control during brake-by-wire control accompanying the driver's braking operation. This enables control of the stroke of piston 52 P of master cylinder 5 and active control of operation of brake pedal 2 . More specifically, when brake operating condition detector 101 detects braking operation, cutoff valve 21 is closed, and the hydraulic pressure generated in first hydraulic line 11 by pump 7 is used to control the hydraulic pressure on wheel cylinders 8 . During this control, to reduce the wheel cylinder pressure under antilock control, SS/V OUT 24 is closed and SS/V IN 23 is opened.
  • SS/V OUT 24 is opened and SS/V IN 23 is closed.
  • SS/V OUT 24 and SS/V IN 23 are closed.
  • the pressure increase, decrease, and hold may be determined on the basis of whether or not the total required amount of brake fluid (hereinafter “the required fluid amount”) calculated from the required brake forces for the plurality of wheels FL to RR (target wheel cylinder hydraulic pressure) is on the decrease or increase.
  • the purpose of this determination it to improve the accuracy with which variations in brake fluid amount used in the whole system 1 under antilock control can be determined. For example, a decreasing total value of required fluid amount can be recognized as a reduction in wheel cylinder hydraulic pressure exerted by the whole system 1 .
  • brake control systems that are capable of cutting off the communication between the master cylinder and wheel cylinders, comprise a mechanism for simulating pedal reaction force (stroke simulator) in addition to the wheel cylinders, and are capable of pressuring the wheel cylinders with the aid of a hydraulic pressure source, apart from the master cylinder.
  • stroke simulator pedal reaction force
  • Such a system normally cuts off the communication between the master cylinder and wheel cylinders and creates pedal reaction force with the aid of a stroke simulator while using a hydraulic pressure source to apply pressure to the wheel cylinders.
  • system 1 of this embodiment uses stroke simulator 22 as a hydraulic pressure source (which operates in response to the driver's brake operation, to simulate pedal reaction force), independent of pump 7 , to supply brake fluid to wheel cylinders 8 .
  • stroke simulator 22 discharges brake fluid from backpressure chamber R 2 on the side opposite to the side of stroke simulator 22 which receives a flow of brake fluid from master cylinder 5 .
  • This outflow of brake fluid is delivered to wheel cylinders 8 to pressurize them. In this way, the rate of pressurization in wheel cylinders 8 can be improved even when the rate of pressurization (pressure response) in wheel cylinders 8 the pump 7 can achieve is insufficient.
  • the pressure response in wheel cylinders 8 is improved by using brake fluid discharged from stroke simulator 22 under the action of the driver's pedal effort (brake fluid supplied independent of pump 7 ).
  • This embodiment uses pump 7 as a hydraulic pressure source and motor 7 a (electric motor) as an actuator for the hydraulic pressure source.
  • the hydraulic pressure source may be any fluid mechanism so long as it is capable of converting mechanical energy (motive power) into brake fluid pressure and holding the pressure.
  • the hydraulic pressure source is not limited to a pump and may be, for example, a piston cylinder, an accumulator, or the like.
  • the actuator may be any mechanism (motor) so long as it is capable of converting an input of electrical energy (electric power) into physical motion (motive power) to actuate the hydraulic pressure source, and is not limited to a motor (electric motor).
  • stroke simulator 22 has the function of a brake fluid source to supply brake fluid to wheel cylinders 8 , as well as its intrinsic function of simulating pedal reaction force. This prevents spongy pedal feel.
  • third hydraulic line 13 is directly connected to a point between cutoff valve 21 P in first hydraulic line 11 P and wheel cylinders 8 .
  • third hydraulic line 13 may be connected indirectly to first hydraulic line 11 P.
  • third hydraulic line 13 may be connected to outlet hydraulic line 16 .
  • the length of the fluid path extending from backpressure chamber R 2 to wheel cylinders 8 is shortened by connecting third hydraulic line 13 directly to first hydraulic line 11 P.
  • third hydraulic line 13 is housed in one unit: unit 61 . This eliminates the need for using a brake line forming third hydraulic line 13 to connect units 61 and 62 and thus simplifies the overall structure of system 1 .
  • Backpressure chamber R 2 of stroke simulator 22 is connected to reservoir tank 4 by fourth hydraulic line 14 .
  • This connection of backpressure chamber R 2 to reservoir tank 4 a lower pressure section, ensures smooth operation of stroke simulator 22 .
  • a switch is provided to switch the path of brake fluid from backpressure chamber R 2 between the path of brake fluid leading to reservoir tank 4 via fourth hydraulic line 14 and the path of brake fluid leading to first hydraulic line 11 P ( 11 B) via third hydraulic line 13 .
  • This enables the destination of brake fluid leaving stroke simulator 22 to be easily switched from the reservoir tank 4 side to the wheel cylinder 8 side and vice versa. This improves the pressure response in wheel cylinders 8 and pedal feel.
  • Third hydraulic line 13 is provided with SS/V IN 23 .
  • SS/V IN 23 forms (part of) the switch.
  • the operation of SS/V IN 23 is controlled to change the state of communication through third hydraulic line 13 , thereby switching on and off the supply of brake fluid from backpressure chamber R 2 to wheel cylinders 8 to switch on and off auxiliary pressure control, as required.
  • SS/V IN 23 is fitted to establish and block the communication between backpressure chamber R 2 and first hydraulic line 11 P.
  • SS/V IN 23 is closed to cut off the communication between backpressure chamber R 2 and first hydraulic line 11 P ( 11 B) and thus make the flow of brake fluid from backpressure chamber R 2 unavailable for auxiliary pressure control. This prevents (or terminates) auxiliary pressure control.
  • opening SS/V IN 23 establishes the communication between backpressure chamber R 2 and first hydraulic line 11 P ( 11 B) to make brake fluid from backpressure chamber R 2 available for auxiliary pressure control to perform auxiliary pressure control.
  • SS/V IN 23 may be of normally open type.
  • Fourth hydraulic line 14 is provided with SS/V OUT 24 .
  • the operation of SS/V OUT 24 is controlled to change the state of communication through fourth hydraulic line 14 to switch on and off the operation of stroke simulator 22 , as required.
  • SS/V OUT 24 is fitted to establish and block the communication between backpressure chamber R 2 and inlet hydraulic line 15 (reservoir tank 4 ).
  • SS/V OUT 24 is closed to block the communication between backpressure chamber R 2 and reservoir tank 4 , thereby preventing the flow of brake fluid from backpressure chamber R 2 to reservoir tank 4 . This prevents piston 220 from undergoing a stroke and keeps stroke simulator 22 inactive.
  • S/V OUT 24 forms (part of) the switch.
  • the operation of SS/V OUT 24 is controlled to change the state of communication through fourth hydraulic line 14 , thereby facilitating auxiliary pressure control. More specifically, SS/V OUT 24 is closed to cut off the communication between backpressure chamber R 2 and reservoir tank 4 to make a larger amount of brake fluid leaving backpressure chamber R 2 available for auxiliary pressure control. When SS/V OUT 24 is opened, the communication between backpressure chamber R 2 and reservoir tank 4 is established to reduce the amount of brake fluid leaving backpressure chamber R 2 for auxiliary pressure control.
  • the auxiliary pressure control can be easily performed by switching the operating state of SS/V OUT 24 and SS/V IN 23 .
  • the combined operation of SS/V OUT 24 and SS/V IN 23 can be controlled, as required, to readily switch between the state of operation of stroke simulator 22 for merely creating pedal reaction force (wheel cylinder pressure control with the aid of pump 7 alone) and the state of operation of stroke simulator 22 for (also) improving the responsiveness of wheel cylinder pressurization (auxiliary pressure control). More specifically, when SS/V OUT 24 is opened, SS/V IN 23 is closed to prevent the hydraulic pressure on the first hydraulic line 11 P side from acting on backpressure chamber R 2 , thereby making the operation of stroke simulator 22 smooth.
  • SS/V IN 23 When SS/V IN 23 is opened, SS/V OUT 24 is closed to prevent brake fluid leaving backpressure chamber R 2 from being discharged onto inlet hydraulic line 15 (reservoir tank 4 ) side and increase the supply of brake fluid via first hydraulic line 11 P into wheel cylinders 8 , thereby improving the pressure response in wheel cylinders 8 .
  • SS/V OUT 24 If SS/V OUT 24 is already used as a solenoid valve for switching on and off the operation of stroke simulator 22 , the mere addition of another solenoid valve, namely, SS/V IN 23 is sufficient to achieve the above-described function, eliminating the need for an additional component or making the system larger or more complex.
  • SS/V OUT 24 is disposed, not on the positive pressure chamber R 1 (second hydraulic line 12 ) side of stroke simulator 22 , but on the backpressure R 2 (fourth hydraulic line 14 ) side, this arrangement improves the pedal feel experienced at the end of auxiliary pressure control. If SS/V OUT 24 were disposed on the positive pressure chamber R 1 side (in second hydraulic line 12 ), the following problem would conceivably occur. In such arrangement, it might appear possible to achieve auxiliary pressure control by supplying brake fluid from master cylinder 5 to wheel cylinders 8 , with SS/V OUT 24 closed and cutoff valve 21 open.
  • piston 220 of stroke simulator 22 continues to undergo a stroke corresponding to the amount of brake fluid flowing from master cylinder 5 in response to braking operation. That means that not only during normal wheel cylinder pressure control with the aid of pump 7 but also during auxiliary pressure control, brake fluid continues to flow into stroke simulator 22 (positive pressure chamber R 1 ) to operate stroke simulator 22 .
  • stroke simulator 22 the stroke of piston 220 , or the amount of deformation of spring 221
  • the amount of operation of stroke simulator 22 corresponds to the pedal stroke at the end of the control.
  • auxiliary pressure control is implemented to improve the pressure response in wheel cylinders 8 . More specifically, provision is made to perform auxiliary pressure control if the driver's brake operation is a predetermined emergency operation and otherwise perform normal wheel cylinder pressure control with the aid of pump 7 .
  • the determination of whether it is an emergency braking operation requires means for measuring or estimating the rate of braking.
  • One conceivable means would be to measure or estimate the change in hydraulic pressure (rate of change) at a predetermined point in hydraulic pressure control unit 6 and use the measured or estimated change to determine or estimate the rate of braking.
  • brake pedals brake actuating members
  • a change in hydraulic pressure is preceded by the displacement of the brake pedal (according to a sensor reading).
  • This phenomenon becomes particularly conspicuous in an emergency braking operation.
  • this embodiment measures or estimates the rate of braking operation on the basis of the displacement (pedal travel) of the brake pedal 2 , rather than the change in hydraulic pressure. This leads to (prompt) determination at earlier state of whether it is an emergency operation and thus improves the pressure response in wheel cylinders 8 effectively.
  • the responsiveness of pressurization in the wheel cylinders 8 by pump 7 is notably insufficient when the performance of pump 7 , supplying brake fluid to wheel cylinders 8 , has not yet reached a sufficient level, that is, when the rotational speed of motor 72 , the actuator of pump 7 , is low.
  • this embodiment performs auxiliary pressure control to improve the pressure response in wheel cylinders 8 effectively in the following manner.
  • a measured or estimated rotational speed Nm of motor 7 a is lower than or equal to set value Nm 0
  • Set value Nm 0 may be such a value that the performance of pump 7 in supplying brake fluid (pressure) is sufficient to apply enough pressure to wheel cylinders 8 .
  • set value Nm 0 is set to a rotational speed that is sufficient for pump 7 to generate a wheel-cylinder hydraulic pressure greater than master cylinder hydraulic pressure.
  • set value Nm 0 is set to a rotational speed that is sufficient for pump 7 to generate a wheel-cylinder hydraulic pressure greater than master cylinder hydraulic pressure.
  • wheel cylinder hydraulic pressure (or its equivalent hydraulic pressure) acts on backpressure chamber R 2 of stroke simulator 22 . It is thus necessary to apply greater pedal effort for the same pedal stroke than that during the normal wheel cylinder pressure control in which atmospheric pressure (a low pressure in reservoir tank 4 ) acts on backpressure chamber R 2 . For this reason, the F-S characteristics are slightly different from that during the normal wheel cylinder pressure control (normal control). Since the auxiliary pressure control takes place when pedal effort is being applied (in a dynamic situation where pedal effort and pedal stroke vary), the difference in the characteristics is permissible to some extent (less likely to give discomfort to the driver). However, an extremely long continuous auxiliary pressure control may give the driver discomfort and deteriorate pedal feel.
  • this embodiment terminates auxiliary pressure control at the instant when motor rotational speed Nm exceeds set value Nm 0 (that is, at early stage). Since the auxiliary pressure control ends before wheel cylinder hydraulic pressure acting on backpressure chamber R 2 becomes excessively high, pedal feel deterioration can be avoided effectively.
  • the condition that the motor rotational speed Nm be lower than or equal to set value Nm 0 may be replaced with a condition that time (according to a timer) that has elapsed since an increase in motor rotational speed command value (in response to a brake pedal stepping operation) be shorter than or equal to a set value.
  • time according to a timer
  • auxiliary pressure control is performed (and when the time elapsed becomes longer than or equal to the set value, the auxiliary pressure control ends).
  • This set value for a timer is set to a length of time required to bring the performance of pump 7 in supplying pressure, to a sufficient level (e.g., when the actual motor rotational speed becomes greater than or equal to a level sufficient for pump 7 to supply wheel cylinder hydraulic pressure greater than master cylinder hydraulic pressure).
  • the set value may be experimentally preset, allowing for a time delay in control by motor 7 a and other factors.
  • the amount of brake fluid Q supplied to the wheel cylinders and the wheel cylinder hydraulic pressure P are so related that the rate ⁇ P/ ⁇ Q (fluid stiffness) of the increase in wheel cylinder hydraulic pressure P relative to the increase in fluid amount Q is low in a certain low pressure region and the ⁇ P/ ⁇ Q is high above the low pressure region, or in a non-low pressure region.
  • the wheel cylinder hydraulic pressure In the low pressure region, the wheel cylinder hydraulic pressure has been low and a large amount of brake fluid is required to increase the wheel cylinder hydraulic pressure, although force required to increase the wheel cylinder hydraulic pressure is low.
  • the wheel cylinder hydraulic pressure In the non-low pressure region, the wheel cylinder hydraulic pressure is developed to some extent and large force is required to increase the wheel cylinder hydraulic pressure, although the amount of brake fluid required to increase the wheel cylinder hydraulic pressure is small.
  • the responsiveness in pressurization in the wheel cylinders by the pump 7 is conspicuously insufficient in the low pressure region.
  • auxiliary pressure control is performed in this low pressure region to improve the pressure response in wheel cylinders 8 effectively.
  • auxiliary pressure control when a pedal stroke S measured is less than or equal to set value S 0 , auxiliary pressure control is performed.
  • auxiliary pressure control an amount of brake fluid corresponding to a stroke of piston 52 of master cylinder 5 (piston 220 of stroke simulator 22 ) is delivered to wheel cylinders 8 .
  • force required to increase the wheel cylinder hydraulic pressure is relatively low, and pedal effort is enough to increase the wheel cylinder hydraulic pressure sufficiently. It is therefore possible to improve the pressure response in wheel cylinders 8 .
  • the low and non-low pressure regions and set value S 0 of pedal stroke S for distinguishing between the two regions may be preset by experiment or the like.
  • a wheel cylinder hydraulic pressure measured by hydraulic sensor 92 may be used to determine whether it is in the low or non-low pressure region. This direct observation of the wheel cylinder hydraulic pressure enables a more reliable determination of whether it is in the low or non-low pressure region than the observation of the pedal stroke (amount of braking) (alternatively, an estimate of wheel cylinder hydraulic pressure may be used for that purpose). More specifically, provision is made to perform auxiliary pressure control when a measured or estimated wheel cylinder hydraulic pressure is less than or equal to a set value, and perform normal wheel cylinder pressure control by pump 7 when the measured or estimated wheel cylinder hydraulic pressure is greater than the set value.
  • this embodiment takes a detected pedal stroke S (amount of braking) into account to determine whether it is in the low or the non-low pressure region. This makes it possible to make a (more prompt) determination at an earlier stage than when taking a measured or estimated wheel cylinder hydraulic pressure into account for the determination, since, as described above, a pedal stroke (as a sensor reading) precedes a change in hydraulic pressure. It is therefore possible to improve the pressure response of in wheel cylinders 8 .
  • pedal stroke S is less than or equal to set value S 0 and the rotational speed Nm of motor 7 a is less than or equal to Nm 0 .
  • stroke simulator 22 is adapted to apply pressure to the wheel cylinders by supplying them with brake fluid from backpressure chamber R (and producing reaction force to the driver's brake operation) as piston 220 moves toward backpressure chamber R.
  • pedal stroke S being less than or equal to S 0 means that the stroke of piston 220 (the amount of displacement from its initial position) is small.
  • Nm being less than equal to Nm 0 means that pedal stroke S is small.
  • stroke simulator 22 is adapted to produce reaction force to the driver's brake operation.
  • spring 221 of stroke simulator 22 applies urging force to piston 220 to produce reaction force to the driver's brake operation.
  • the urging force (spring constant) of spring 221 is set to a value that enables spring 221 to produce reaction force to the driver's brake operation, according to pedal stroke S, at least when piston 220 undergoes a large stroke (when spring 221 experiences a large compression).
  • Hydraulic pressure control unit 6 of this embodiment is capable of putting stroke simulator 22 into operation under the action of hydraulic pressure generated by pump 7 by controlling the operation of SS/V OUT 24 and SS/V IN 23 , so as to impart a stroke to piston 52 P of master cylinder 5 , even during brake-by-wire control in which master cylinder 5 is cut off from wheel cylinders 8 by closing cutoff valve 21 . That is, by closing SS/V OUT 24 and opening SS/V IN 23 , brake fluid is supplied to backpressure chamber R 2 of stroke simulator 22 through third hydraulic line 13 from first hydraulic line 11 P (hydraulic line 11 B), which is pressurized by pump 7 .
  • pedal stroke and pedal reaction force can be properly controlled.
  • SS/V OUT 24 is closed and SS/V IN 23 is opened, so as to reverse the direction of movement of brake pedal 2 and move it back toward its initial position.
  • This makes it possible to create a response of brake pedal 2 that approximates a response created by a conventional brake control system, which transmits changes in hydraulic pressure in the wheel cylinders during antilock control to the master cylinder (brake pedal). The pedal feel so created thus hardly gives discomfort.
  • brake pedal 2 is moved by the distance corresponding to the amount of brake fluid required by wheel cylinders 8 (according to road frictional force). This allows the driver to use the position of the brake pedal 2 to estimate road frictional force (adhesion limit). For example, by properly setting the length of time in which valves 23 and 24 open, pedal stroke is made to decrease with decreasing road frictional force.
  • SS/V OUT 24 is opened and SS/V IN 23 is closed. In this way, the pedal feel experienced during normal braking can be provided immediately upon the end of the antilock control. Thus the pedal feel hardly gives discomfort.
  • FIG. 4 schematically shows the structure of system 1 of the second embodiment.
  • This system 1 is different from that of the first embodiment, in that check valve 230 is used, instead of stroke simulator IN valve SS/V IN 23 (solenoid valve), in third hydraulic line 13 .
  • Hydraulic pressure control unit 6 comprises first unit 63 and second unit 64 .
  • First unit 63 is a pump unit comprising pump 7 and motor 7 a .
  • Second unit 64 is a valve unit housing valves 21 for opening and closing hydraulic line 11 , etc.
  • Second unit 64 comprises stroke simulator 22 and sensors 90 to 93 and is formed integral with master cylinder 5 .
  • Second unit 64 is integrated with reservoir tank 4 .
  • master cylinder 5 and stroke simulator 22 are housed in the same housing to form a master cylinder unit.
  • Reservoir tank 4 and pump 7 are integrated with the master cylinder unit to form a single unit as a whole.
  • the valve unit is integrated with the master cylinder unit to form a single unit as a whole.
  • Master cylinder 5 , stroke simulator 22 , valve 21 , etc. are housed in the same housing.
  • First unit 63 is provided therein with fluid reservoir 15 A of a set volume above inlet hydraulic line 15 .
  • Fluid reservoir 15 A is a reservoir inside hydraulic pressure control unit 6 .
  • Fluid reservoir 15 A is located in first unit 63 near a point of connection (on the vertically top side of first unit 63 ) with a brake pipe forming inlet hydraulic line 15 .
  • First and second pressure reducing hydraulic lines 17 and 18 are connected to fluid reservoir 15 A.
  • Pump 7 draws brake fluid from reservoir tank 4 via fluid reservoir 15 A.
  • Brake fluid in fourth hydraulic line 14 returns via fluid reservoir 15 A to reservoir tank 4 .
  • Check valve 230 is a one-way valve that admits only the flow of brake fluid from the backpressure chamber R 2 side to the first hydraulic line 11 side.
  • Third hydraulic line 13 is divided by check valve 230 into hydraulic line 13 A on the backpressure chamber R 2 side and hydraulic line 13 B on the first hydraulic line 11 side.
  • Fourth hydraulic line 14 is provided with constriction 24 A, instead of a solenoid valve (stroke similar OUT valve SS/V OUT 24 ).
  • Constriction 24 is a resisting portion having a set fluid path resistance. The amount constricted by constriction 24 (amount of reduction in flow path cross section) is set larger than the amount constricted by check valve 230 when it is opened.
  • constriction 24 A is set larger than that of check valve 230 when open.
  • Constriction 24 A is bypassed by bypass hydraulic line 140 , which is disposed in parallel to fourth hydraulic line 14 .
  • Bypass hydraulic line 14 is provided with check valve 240 that admits only the flow from the inlet hydraulic line 15 side to the third hydraulic line 13 (hydraulic line 13 B) side.
  • Wheel-cylinder hydraulic pressure controller 104 unlike that of the first embodiment, does not comprise auxiliary pressure controller 105 . While wheel-cylinder hydraulic pressure controller 104 performs normal boost control (wheel cylinder pressure control by pump 7 ), auxiliary pressure control starts automatically (or stops automatically) In other words, wheel-cylinder hydraulic pressure controller 104 doubles as an auxiliary pressure controller. Since other elements are the same as those of the first embodiment, description of the other elements is omitted by using the same reference numerals as those of the first embodiment.
  • Booster 3 connects brake pedal 2 and pushrod 30 and boosts pedal effort and transmits it to pushrod 30 .
  • Booster 3 is capable of mechanically transmitting force between brake pedal 2 and master cylinder 5 and is a link-type booster with variable boost ratio.
  • Booster 3 comprises a link mechanism that varies the ratio of stroke of pushrod 30 to pedal stroke (lever ratio).
  • This link mechanism comprises first link 31 of a rod shape in side view and second link 32 of a triangular shape in side view.
  • First link 31 is pivotally connected at one end to the root of brake pedal 2 (pedal arm).
  • Second link 32 has a first apex rotatably supported on the vehicle body.
  • First link 31 is pivotally connected at the other end to a second apex of second link 32 .
  • Second link 32 has a third apex pivotally connected to one axial end of pushrod 30 .
  • Pushrod 30 receives force from second link 32 and undergoes a stroke in accordance with depression of brake pedal 2 .
  • Pushrod 30 transmits pedal effort transmitted through (and boosted by) booster 3 as an axial thrust to master cylinder 5 (primary piston 52 P).
  • Stroke sensor 90 is housed in master cylinder 5 to measure the stroke of primary piston 52 P (pushrod 30 ) as an amount of brake operation by the driver.
  • Hydraulic pressure sensor 93 which measures pump outlet pressure, is located in outlet hydraulic line 16 between outlet 71 of pump 7 (check valve 160 ) and communication valve 26 .
  • hydraulic pressure sensor 93 may be provided in first pressure reducing hydraulic line 17 between connection point P 1 with outlet hydraulic line 16 and pressure regulating valve 27 .
  • Booster 3 may be omitted or replaced with other type of booster, depending on a set lever ratio and other properties.
  • Check valve 230 and constriction 24 A automatically (without being directly controlled) carries out the control that would otherwise be performed by auxiliary pressure controller 105 of the first embodiment (starts, performs, and ends auxiliary pressure control).
  • Third hydraulic line 13 is provided with check valve 230 that admits only the flow of brake fluid from backpressure chamber R 2 to wheel cylinder 8 .
  • Check valve 230 forms (part of) a switch that switches brake fluid coming from backpressure chamber R 2 between a path leading via fourth hydraulic line 14 to reservoir tank 4 and a path leading via third hydraulic line 13 to first hydraulic line 11 P ( 11 B)
  • check valve 230 opens to allow brake fluid from backpressure chamber R 2 to flow via third hydraulic line 13 into first hydraulic line 11 P ( 11 B). This makes it possible to start and perform auxiliary pressure control automatically.
  • check valve 230 When the hydraulic pressure on the first hydraulic line 11 P ( 11 B) side of check valve 230 is higher than that on the backpressure chamber R 2 side, check valve 230 closes to prevent brake fluid coming from backpressure chamber R 2 from flowing via third hydraulic line 13 into first hydraulic line 11 P ( 11 B). This automatically ends the auxiliary pressure control.
  • Fourth hydraulic line 14 is provided with constriction 24 A.
  • Forth hydraulic line 14 admits both the flow of brake fluid from backpressure chamber R 2 and the flow of brake fluid from reservoir tank 4 .
  • Forth hydraulic line 14 does not have a solenoid valve or check valve that would, depending on the operating state of such a valve, impede a flow of brake fluid through fourth hydraulic line 14 , and thus facilitates the flow. This makes, for example, the operation of stroke simulator 22 smooth.
  • Constriction 24 A forms (part of) the switch. Constriction 24 has a set constriction resistance. This facilitates path switching by the switch and hence auxiliary pressure control.
  • the flow rate of brake fluid leaving backpressure chamber R 2 is high in an emergency brake operation than that in a non-emergency brake operation; thus, the difference in hydraulic pressure (pressure differential) between the backpressure chamber R 2 side of constriction 24 A and the reservoir tank 4 side is larger in an emergency brake operation.
  • the resultant increase in the flow rate through constriction 24 A in emergency braking is smaller than that in non-emergency braking. For this reason, in emergency braking, of the amount of brake fluid leaving backpressure chamber R 2 , the amount of brake fluid flowing through fourth hydraulic line 14 into reservoir tank 4 is reduced to make a larger amount of brake fluid available for auxiliary pressure control.
  • non-emergency braking In non-emergency braking, the flow rate of brake fluid leaving backpressure chamber R 2 is low and the difference in hydraulic pressure is small. This makes an increase in flow rate through constriction 24 A, due to a given increase in the difference in hydraulic pressure, larger in non-emergency braking than that due to the same increase in the difference in hydraulic pressure in emergency braking. For this reason, in non-emergency braking, of the amount of brake fluid leaving backpressure chamber R 2 , the amount of brake fluid flowing through fourth hydraulic line 14 into reservoir tank 4 can be increased.
  • FIGS. 5 and 6 are enlarged schematic views of second to fourth hydraulic lines 12 to 14 .
  • the flow of brake fluid leaving backpressure chamber R 2 of stroke simulator 22 in the driver's non-emergency brake operation is indicated by an arrow.
  • FIG. 6 uses an arrow to indicate the flow of brake fluid leaving backpressure chamber R 2 in the driver's emergency operation.
  • wheel-cylinder hydraulic pressure controller 104 controls the wheel cylinder hydraulic pressure to a value higher than the master cylinder hydraulic pressure corresponding to a pedal stroke, so as to attain a set boost ratio.
  • the movement of piston 220 of stroke simulator 22 is not fast. This makes the pressure differential through constriction 24 A very small, preventing the hydraulic pressure in hydraulic line 13 A on the backpressure chamber R 2 side from increasing.
  • the rate of pressure increase in wheel cylinders 8 by pump 7 (pressure response) relative to the rate of brake operation is sufficiently large. This enables the wheel cylinder hydraulic pressure to rise above the master cylinder hydraulic pressure.
  • the hydraulic pressure in hydraulic line 13 B of third hydraulic line 13 on the first hydraulic line 11 is higher than that in hydraulic line 13 A on the backpressure chamber R 2 side.
  • check valve 230 is closed (sealed).
  • brake fluid flowing from backpressure chamber R 2 into hydraulic line 13 A does not flow through check valve 230 into hydraulic line 13 B and flow through constriction 24 A into fourth hydraulic line 14 and then toward reservoir tank 4 .
  • auxiliary pressure control is not performed and only wheel cylinder pressure control is performed by pump 7 . All of brake fluid leaving backpressure chamber R 2 is released toward reservoir tank 4 , so that stroke simulator 22 functions only to produce reaction force to the driver's brake operation.
  • the difference in hydraulic pressure across check valve 230 between the first hydraulic pressure line 11 (hydraulic line 13 B) side of third hydraulic line 13 and the backpressure chamber R 2 (hydraulic line 13 A) side is lower than or equal to that across constriction 24 A between the reservoir tank 4 side of fourth hydraulic chamber 14 and the backpressure chamber R 2 side.
  • wheel cylinders 8 are hardly pressurized by pump 7 (e.g., when the hydraulic pressure in hydraulic line 13 B is low and substantially equal to atmospheric pressure)
  • the amount constricted by constriction 24 A is set larger than the amount constricted by check valve 230 when open. In other words, brake fluid flows more readily through check valve 230 than through constriction 24 A.
  • the amount of fluid Q 2 through constriction 24 is exceeded by the amount of fluid Q 1 through check valve 230 .
  • the flow rate of brake fluid leaving backpressure chamber R 2 is higher than that in a non-emergency brake operation, and the higher flow rate results in a reduction in the amount of fluid Q 2 through constriction 24 A.
  • the amount of fluid Q 0 is larger than that in non-emergency braking.
  • a certain amount of fluid Q 1 namely the difference between the amount of fluid Q 0 and the amount of fluid Q 2 , is sent through hydraulic line 13 B into first hydraulic line 11 and is used to pressurize wheel cylinders 8 .
  • check valve 230 opens when the rate of pressure increase (pressure response) in wheel cylinders 8 by pump 7 for a given speed of depression of the brake pedal is insufficiently and the hydraulic pressure in hydraulic line 13 B on the wheel cylinder 8 side is lower than that in hydraulic line 13 A on the backpressure chamber R 2 side.
  • This (relative) decrease in hydraulic pressure on the wheel cylinder 8 side becomes conspicuous when the pedal stroke S is small (when motor 7 A just starts running).
  • a small pedal stroke S means a small stroke of piston 220 of stroke simulator 22 .
  • Stroke simulator 22 is adapted to pressurize wheel cylinders 8 , at least by transmitting brake fluid from backpressure chamber R to wheel cylinders 8 (while producing reaction force to the driver's brake operation) when the stroke of piston 220 is small. On the other hand, at least when the stroke of piston 220 is large, stroke simulator 22 produces reaction force to the driver's brake operation.
  • a flow of brake fluid from backpressure chamber R 2 induced by the driver's emergency brake operation is used to generate wheel cylinder hydraulic pressure. This makes it possible to improve the pressure response in wheel cylinders 8 .
  • check valve 230 opens automatically and allows brake fluid to flow from backpressure chamber R 2 into wheel cylinders 8 .
  • This mechanical actuation of check valve 230 induced by a difference in hydraulic pressure switches on and off auxiliary pressure control.
  • the use of check valve 230 improves response more effectively than when a solenoid valve is used that would cause a delay in response for auxiliary pressure control, and also prevents pedal feel deterioration.
  • brake fluid would return from the wheel cylinder 8 (hydraulic line 13 B) side to the backpressure chamber R 2 (hydraulic line 13 A) side when the solenoid valve is left open even through the hydraulic pressure on the wheel cylinder 8 (hydraulic line 13 B) side exceeds that on the master cylinder 5 (hydraulic line 13 A) side; this might result in a reduction in pressure response in wheel cylinders 8 and an increase in master cylinder hydraulic pressure.
  • Constriction 24 A in fourth hydraulic line 14 may be replaced with a solenoid valve.
  • SS/V IN 23 in third hydraulic line 13 of the first embodiment may be replaced with check value 230 as used in this embodiment.
  • check valve 230 automatically opens. This eliminates the trouble of controlling SS/V IN 23 and still brings about the above-described effect.
  • brake fluid from backpressure chamber R 2 can be prevented from leaking through the solenoid valve in fourth hydraulic line 14 toward reservoir tank 4 , supplying brake fluid into the wheel cylinders more effectively.
  • constriction 24 A rather than a solenoid valve, avoids the effect arising from a delay in response for control that would be caused by the solenoid valve in fourth hydraulic line 14 . It is possible, for example, to prevent a delay in closing a solenoid valve in fourth hydraulic line 14 at the end of auxiliary pressure control would obstruct movement of piston 220 in stroke simulator 22 and deteriorate brake feel. It is also possible to prevent a reduction in brake fluid supplied to the wheel cylinder 8 (hydraulic line 13 B) side that would result in a insufficient improvement in response if a delay in closing the solenoid valve in fourth hydraulic line 14 occurred at the beginning of auxiliary pressure control.
  • Constriction 24 A is bypassed by bypass hydraulic line 140 with check valve 240 .
  • This makes smooth the flow of brake fluid from the reservoir tank 4 side through bypass hydraulic line 140 to the backpressure chamber R 2 (hydraulic line 13 A) side. Since this facilitates an increase in the volume of backpressure chamber R 2 , piston 220 moves smoothly in stroke simulator 22 toward positive pressure chamber R 1 when brake pedal 2 moves back during brake-by-wire control. Thus, while stroke simulator 22 returns to its initial state of operation, brake pedal 2 moves back promptly.
  • fluid reservoir 15 A can be used as a source of brake fluid and a reservoir to which brake fluid is returned, so as to continue boost control (to raise or drop the wheel cylinder hydraulic pressure) with the aid of pump 7 and auxiliary pressure control.
  • boost control to raise or drop the wheel cylinder hydraulic pressure
  • the volume of fluid reservoir 15 A is set to a value which allows brake control to continue to some extent.
  • Other details of the second embodiment are the same as those of the first embodiment and bring about the same effect as that of the first embodiment.
  • FIG. 7 is a schematic view of the structure of system 1 of the third embodiment.
  • System 1 of this embodiment is different from that of the second embodiment, in that third hydraulic line 13 of the former is provided with stroke simulator IN valve SS/V IN 23 , which is a normally open on/off solenoid valve.
  • Third hydraulic line 13 is divided by SS/V IN 23 into hydraulic line 13 A on the backpressure chamber R 2 side and hydraulic line 13 B on first hydraulic line 11 side.
  • SS/V IN 23 is bypassed by bypass hydraulic line 130 , running parallel to third hydraulic line 13 .
  • Bypass hydraulic line 130 connects hydraulic line 13 A and hydraulic line 13 B.
  • Bypass hydraulic line 130 is provided with check valve 230 , which admits only the flow of brake fluid flowing from the backpressure chamber R 2 (hydraulic line 13 A) side to the first hydraulic line 11 (hydraulic line 13 B) side.
  • wheel-cylinder hydraulic pressure controller 104 closes SS/V IN 23 .
  • wheel-cylinder hydraulic pressure controller 104 controls SS/V 23 in accordance with the state of antilock control to control the operation of stroke simulator 22 . More specifically, to reduce the wheel cylinder hydraulic pressure under antilock control while hydraulic pressure generated in first hydraulic line 11 by pump 7 is used to control the hydraulic pressure in wheel cylinders 8 , SS/V IN 23 is opened. To increase or hold the wheel cylinder hydraulic pressure, SS/V IN 23 is closed. Since other elements of this embodiment are the same as those of the second embodiment, description of the other elements is omitted by assigning the same reference numerals to them.
  • check valve 230 In emergency brake operation during boost control, the hydraulic pressure on the downstream side (hydraulic line 13 B side) of check valve 230 generated by pump 7 may drop below the pressure of brake fluid leaving backpressure chamber R 2 (the hydraulic pressure in hydraulic line 13 A). In such a case, check valve 230 opens. At least part of hydraulic fluid coming from backpressure chamber R 2 is delivered through third hydraulic line 13 toward wheel cylinder 8 . Meanwhile, stroke simulator 23 serves not only to generate reaction force to the brake operation but also to perform the auxiliary pressurization function.
  • ECU 100 may be designed to open SS/V IN 23 while the driver's brake operation is recognized as a predetermined emergency one, that is, while the rate of pressurization in wheel cylinders 8 with the aid of pump 7 (pressure response) may become insufficient.
  • wheel cylinders 8 are supplied, during the predetermined emergency brake operation, with brake fluid, not only through check valve 230 from backpressure chamber R 2 but also through SS/V IN 23 . In this way, wheel cylinders 8 are supplied with a greater amount of brake fluid to improve the rate of increase in pressure in wheel cylinders 8 .
  • brake pedal 2 can be actively controlled by controlling SS/V IN 23 in accordance with the state of antilock control during brake-by-wire control. More specifically, when reducing the wheel cylinder hydraulic pressure, SS/V IN 23 is opened so that the high pressure on the pump 7 side acts on piston 52 P of master cylinder 5 . Brake fluid from third hydraulic line 13 escaping through fourth hydraulic line 14 toward reservoir 4 is reduced by constriction 24 A. This enables pedal reaction force to increase, imparting a stroke in the return direction of brake pedal 2 . When SS/V IN 23 is closed during an increase in wheel cylinder hydraulic pressure, the high pressure on the pump 7 side is prevented from acting on piston 52 P of master cylinder 5 .
  • FIG. 8 is a schematic view of system 1 of the fourth embodiment. Unlike the second embodiment, brake pedal 2 and master cylinder 5 are not provided with booster 3 therebetween. An in the first embodiment, brake pedal 2 is directly connected to one end of pushrod 30 . Stroke sensor 90 is fitted on brake pedal 2 . Fourth hydraulic line 14 is provided with stroke simulator OUT valve SS/V OUT 24 , which is a normally closed on/off solenoid valve. System 1 of this embodiment is different from that of the second embodiment, in that constriction 24 A of this embodiment is in series with SS/V OUT 24 . Constriction 24 A is provided on the inlet hydraulic line 15 side of SS/V OUT 24 . Bypass hydraulic line 140 bypasses SS/V OUT 24 and constriction 24 A. During boost control, wheel-cylinder hydraulic pressure controller 104 opens SS/V OUT 24 .
  • FIG. 9 is a flowchart of control by ECU 100 . This process is repeated at a set frequency.
  • brake operating condition detector 101 detects pedal stroke S, and the process goes to step S 12 .
  • calculator 102 for calculating a target wheel cylinder hydraulic pressure calculates a target wheel cylinder hydraulic pressure.
  • step S 13 determines whether pedal stroke S is below set value S 1 .
  • Set value S 1 is set to a value greater than zero and less than set value S 2 .
  • Set value S 2 represents pedal stroke S (the upper limit of an idle stroke) over which the outer circumferential surface of piston 52 of master cylinder 5 , which has not been in contact with first piston seal 541 , comes into contact with it.
  • Target wheel cylinder pressure Pw* is such a value that the wheel cylinder pressure starts developing at the same time as the master cylinder pressure does, that is, Pw* becomes greater than zero when S exceeds S 2 . If S is determined to be lower than S 1 , the process goes to step S 14 . If S is determined to be greater than S 1 , the process goes to step S 15 .
  • step S 14 to perform boost control, the following actuators are made inactive: cutoff valve 21 is made inactive (opened), communication valve 26 inactive (closed), SS/V OUT 24 inactive (closed), pump 7 inactive, and pressure regulating valve 27 inactive (opened). Subsequently, this control cycle is terminated.
  • step S 15 boost control is prepared by activating some of the actuators for performing the boost control. More specifically, wheel-cylinder hydraulic pressure controller 104 activates (closes) cutoff valve 21 , activates (opens) communication valve 26 , and activates (opens) SS/V OUT 24 .
  • step S 16 wheel-cylinder hydraulic pressure controller 104 determines whether target wheel cylinder hydraulic pressure Pw* is greater than zero. If yes, the process goes to step S 17 . If it is zero, the process goes to step S 18 .
  • step S 17 some other actuators for performing boost control are activated for boost control. More specifically, wheel-cylinder hydraulic pressure controller 104 activates pump 7 and activates (closes) pressure regulating valve 27 to perform escape control. Then this control cycle ends.
  • step 18 S some other actuators for performing boost control are deactivated to keep the state in which boost control is prepared to start. More specifically, wheel-cylinder hydraulic pressure controller 104 deactivates pump 7 and pressure regulating valve 27 (opened), and this control cycle ends. Since other elements of this embodiment are the same as those of the second embodiment, their description is omitted by assigning the same reference numerals.
  • SS/V OUT 24 in fourth hydraulic line 14 brings about the same effect as that of the first embodiment.
  • SS/V OUT 24 is bypassed by bypass hydraulic line 140 with check valve 240 .
  • This allows brake fluid to flow smoothly from the reservoir tank 4 side through bypass line 140 to the backpressure chamber R 2 (hydraulic line 13 A) side, regardless of the state of operation of SS/V OUT 24 .
  • This avoids the effect of a response delay in control of SS/V OUT 24 and allows brake pedal 2 to promptly move backward during brake-by-wire control (including boost control).
  • wheel-cylinder hydraulic pressure controller 104 opens SS/V OUT 24 . This puts third and fourth hydraulic lines 13 and 14 in the same configuration as that of the second embodiment, and the same effect can be obtained.
  • FIG. 10 is a time chart of operation of system 1 when the driver performs normal brake pedal operation.
  • the driver starts brake pedal operation.
  • pedal force F rises from zero.
  • pedal stroke S becomes greater than zero, and brake operating condition detector 101 recognizes the driver's brake operation.
  • pedal stroke S continues to increase approximately in correspondence to increasing pedal force F.
  • pedal stroke S is held.
  • Predetermined value F 0 is the lower limit of pedal force F (the upper limit of idle pedal force) at which pedal force F actually starts to contribute to (increase) pedal stroke S.
  • interval (i) is an idle pedal force interval. From t 12 , when F exceeds F 0 , the idle pedal force interval ends, and pedal stroke S increases with increasing pedal force F. At t 14 , S reaches S 2 . When S is less than S 2 , the flow of brake fluid from hydraulic chamber 51 into inlet port 502 (reservoir tank 4 ) is not restricted, and hydraulic pressure (master cylinder pressure) is not generated in hydraulic chamber 51 . In other words, intervals (i) and (ii) from t 12 to t 14 are idle stroke intervals. From time t 11 to t 13 , S is less than S 1 . In the flowchart of FIG. 9 , step S 13 is followed by S 14 to deactivate the actuators for performing boost control.
  • step S 13 After t 13 , S exceeds S 1 . Then step S 13 is followed by S 15 to activate some of the above-described actuators to prepare for the start of boost control. Up to t 14 , the target wheel cylinder pressure Pw* is zero. Then step S 16 is followed by S 18 so that the boost controls remains ready to start. Interval (ii) from t 13 to t 14 is a boost control preparation interval. From t 14 , Pw* becomes greater than zero and continues to increase until t 19 . Then S 16 is followed by S 17 to perform boost control. Interval (iii) from t 14 is a boost control interval.
  • FIG. 11 is a time chart of operation of system 1 when the driver performs rapid brake pedal operation. This operation is different from that of FIG. 10 in the following manner. From t 11 to t 17 , pedal force F and pedal stroke S increase. From t 14 , boost control starts. Immediately after the start of boost control in an emergency brake operation, the pressure in wheel cylinders 8 cannot be increased by pump 7 as fast as a rapid increase in Pw* corresponding to an increase in pedal stroke S. As a result, hydraulic pressure P B in hydraulic line 13 B generated by pump 7 is lower than Pw*. In the emergency, the rate of brake fluid flowing from backpressure chamber R 2 into hydraulic line 13 A is high, and the pressure differential across constriction 24 A rises.
  • the hydraulic pressure (hydraulic pressure P A in hydraulic line 13 A) on the upstream side of constriction 24 A (on the backpressure chamber R 2 side) increases in accordance with increasing pedal stroke S.
  • P B is lower than or equal to P A , such that check valve 230 is opened to allow brake fluid to flow from backpressure chamber R 2 through third hydraulic line 13 (check valve 230 ) toward wheel cylinders 8 .
  • Interval (iv*) from t 14 to t 14 is an auxiliary pressure control.
  • P B exceeds P A .
  • check valve 230 closes and the auxiliary pressure control ends.
  • P E rises up to Pw*.
  • SS/V OUT 24 may be opened and kept in that state.
  • SS/V OUT 24 may be closed. This prevents brake fluid leaving backpressure chamber R 2 from leaking through SS/V OUT 24 toward reservoir tank 4 and enables an efficient supply of brake fluid into wheel cylinders 8 .
  • movement of piston 220 in stroke simulator 22 after the end of auxiliary pressure control which would deteriorate pedal feel, can be prevented, for example by opening SS/V OUT 24 before closing check valve 230 .
  • SS/V OUT 24 is opened in the auxiliary pressure control (emergency braking) as well as in normal wheel cylinder pressure control (non-emergency braking). This eliminates the need for opening or closing SS/V OUT 24 at the start or end of auxiliary pressure control, improving the noise/judder characteristics of system 1 .
  • Constriction 24 in fourth hydraulic line 14 may be provided on the third hydraulic line 13 side of SS/V OUT 24 , rather than on the inlet hydraulic line 15 side.
  • the other details of this embodiment are the same as those of the first and second embodiments and bring about the same effect as those of the first and second embodiments.
  • FIG. 12 is a schematic view of system 1 of the fifth embodiment.
  • third hydraulic line 13 is provided with SS/V IN 23 , bypass line 130 , and check valve 230 .
  • Fourth hydraulic line 14 is provided with stroke simulator OUT valve SS/V OUT 24 , which is a normally closed on/off solenoid valve, and constriction 24 in series, as in the fourth embodiment.
  • This embodiment combines the third and fourth embodiments.
  • wheel-cylinder hydraulic pressure controller 104 controls SS/V IN 23 and SS/V OUT 24 .
  • SS/V IN 23 is closed and SS/V OUT 24 opened.
  • the other elements are the same as those of the fourth embodiment, and their description is omitted by assigning the same reference numerals.
  • This embodiment structurally similar to the third and fourth embodiments, brings about a similar effect to that of the third and fourth embodiment.
  • SS/V IN 23 is closed and SS/V OUT 24 opened.
  • FIG. 13 is a schematic view of system 1 of the sixth embodiment.
  • third hydraulic line 13 is provided with a stroke simulator IN valve SS/V IN 23 , which is a normally closed on/off solenoid valve.
  • System 1 of this embodiment is different from that of the first embodiment, in that SS/V IN 23 of the former is in series with constriction 23 A.
  • Third hydraulic line 13 is divided by SS/V IN 23 into hydraulic line 13 A on the backpressure chamber R 2 side and hydraulic line 13 B on the first hydraulic line 11 side.
  • Constriction 23 A is provided on the first hydraulic line 11 (hydraulic line 13 B) side of SS/V IN 23 .
  • fourth hydraulic line 14 is providing with SS/V OUT 24 , constriction 24 A, and bypass line 140 (check valve 240 ). The amount constricted by constriction 24 A is larger than that by constriction 23 A.
  • wheel-cylinder hydraulic pressure controller 104 opens SS/V OUT 24 during boost control.
  • Wheel-cylinder hydraulic pressure controller 104 has auxiliary pressure controller 105 .
  • Auxiliary pressure controller 105 performs auxiliary pressure control in accordance with the driver's brake operation during boost control. More specifically, auxiliary pressure controller 105 determines whether the driver's brake operation is for a predetermined emergency. If so (the speed of depression of brake pedal 2 is high), auxiliary pressure controller 105 opens SS/V IN 23 . If not (the speed of depression of brake pedal 2 is not high), auxiliary pressure controller 105 closes SS/V IN 23 .
  • FIG. 14 is a flowchart of control of ECU 100 . This process is repeated at a set frequency. Steps S 101 to S 103 and S 105 are the same as steps S 11 to S 13 and S 15 of the fourth embodiment ( FIG. 9 ).
  • step S 104 the actuators for performing boost control are deactivated. Specifically, SS/V IN 23 is deactivated (closed). Other actuators are controlled as in step S 14 .
  • step S 106 auxiliary pressure controller 105 determines whether pedal stroke speed ⁇ S/ ⁇ t is greater than or equal to first set value ⁇ . ⁇ is a ⁇ S/ ⁇ t threshold for permitting operation of SS/V IN 23 (performing auxiliary pressure control).
  • step S 107 determines whether motor rotational speed Nm is less than or equal to set valve Nm 0 and pedal stroke S is less than or equal to set valve S 0 . If yes, the process goes to step S 108 . If Nm is greater than Nm 0 or S is greater than S 0 , the process goes to step S 110 . In step S 108 , auxiliary pressure controller 105 activates (opens) SS/V IN 23 , and the process goes to S 111 .
  • step S 109 auxiliary pressure controller 105 determines whether pedal stroke speed ⁇ S/ ⁇ t is less than or equal to second set valve ⁇ ( ⁇ ). ⁇ is a ⁇ S/ ⁇ t threshold for ending operation of SS/V IN 23 (auxiliary pressure control). If yes, the process goes to step S 110 . If no, the process goes to S 111 . In step S 110 , SS/V IN 23 is deactivated (closed), and the process goes to step S 111 . Steps S 111 to S 113 are the same as steps S 16 to S 18 of the fourth embodiment ( FIG. 9 ). Since other elements of this embodiment are the same as those of the fourth embodiment, their description is omitted by assigning the same reference numerals.
  • Third hydraulic line 13 is provided with SS/V IN 23 .
  • SS/V IN 23 forms (part of) a switch for sending brake fluid coming from backpressure chamber R 2 to either the flow path leading via fourth hydraulic line 14 to reservoir tank 4 or the flow path leading via third hydraulic line 13 to first hydraulic line 11 P ( 11 B).
  • SS/V IN 23 may be a normally open one.
  • Fourth hydraulic line 14 is provided with constriction 24 A and SS/V OUT 24 . Constriction 24 A and SS/V OUT 24 form part of the switch, as in the second and fourth embodiments.
  • wheel-cylinder hydraulic pressure controller 104 opens SS/V OUT 24 .
  • auxiliary pressure controller 105 closes SS/V IN 23 .
  • FIG. 15 is a time chart of operation of system 1 when the driver performs normal brake operation.
  • pedal stroke S exceeds S 1 .
  • step S 103 is followed by S 105 to activate some of the actuators for performing boost control and prepare for boost control.
  • step S 106 is followed by S 109 to deactivate (close) SS/V IN 23 .
  • the remainder of operation is the same as that of the fourth embodiment ( FIG. 10 ).
  • auxiliary pressure controller 105 opens SS/V IN 23 .
  • the hydraulic pressure in hydraulic line 13 B on the first hydraulic line 11 side of third hydraulic line 13 drops significantly lower than that in hydraulic line 13 A on the backpressure chamber R 2 side.
  • Brake fluid flowing from backpressure chamber R 2 into hydraulic line 13 A flows through constriction 23 A into hydraulic line 13 B and into first hydraulic line 11 P ( 11 B) and is used to increase the pressure in wheel cylinders 8 . In this way, auxiliary pressure control is performed.
  • constriction 24 A The amount constricted by constriction 24 A is set larger than that by constriction 23 A, making it easier for brake fluid to flow through constriction 23 A than constriction 24 A.
  • brake fluid coming from backpressure chamber R 2 is preferentially sent toward wheel cylinders 8 .
  • the path of brake fluid flowing from backpressure chamber R 2 in response to the driver's brake operation (pedal effort) is switched to the path leading through third hydraulic line 13 to first hydraulic line 11 P ( 11 B).
  • auxiliary pressure controller 105 determines that emergency braking has ended or auxiliary pressure control is no longer necessary, it closes SS/V IN 23 . This switches the path of brake fluid from backpressure chamber R 2 to the path leading via fourth hydraulic line 14 to reservoir tank 4 .
  • FIG. 16 is a time chart of operation of system 1 when the driver performs rapid brake pedal operation.
  • boost control is prepared.
  • the rate of pedal depression is high ( ⁇ S/ ⁇ t is greater than or equal to a)
  • Pedal stroke S is less than or equal to S 0
  • motor rotational speed Nm is less than or equal to Nm 0 .
  • the process goes from step S 106 to step S 107 and then to S 108 to activate (open) SS/V IN 23 .
  • other actuators for performing boost control are activated to perform boost control.
  • Third hydraulic line 13 may dispense with constriction 23 A. Since this embodiment uses constriction 23 A, it is possible to prevent brake fluid from flowing back from the wheel cylinder 8 (hydraulic line 13 B) side toward backpressure chamber R 2 (hydraulic line 13 A) even when SS/V IN 23 is closed after the hydraulic pressure on the upstream side of constriction 23 A (on the backpressure chamber R 2 side) drops below that on the downstream side (on the first hydraulic line side 11 a ). As the pressure differential across constriction 23 A increases, the amount of brake fluid passing constriction 23 A decreases.
  • SS/V IN 23 may be omitted.
  • the use of SS/V IN 23 which shuts communication through hydraulic line 13 B, ensures more reliably to prevent reverse flow of brake fluid to the backpressure chamber R 2 side. This in turn prevents pedal feel deterioration more effectively.
  • SS/V IN 23 may be opened and kept in that state (and SS/V IN 23 is closed for non-emergency braking during brake-by-wire control).
  • Constriction 23 in third hydraulic line 13 may be provided on the backpressure chamber R 2 side of SS/V IN 23 , instead of on the first hydraulic line 11 side.
  • Other details are the same as those of the first and fourth embodiments and bring about the same effect.
  • the brake control system (brake system) of the present invention is not limited to those of the embodiment and may be any other brake control system as long as it comprises a mechanism (stroke simulator) for approximating reaction force to pedal operation and uses a hydraulic pressure source, other than the master cylinder, to apply pressure to the wheel cylinders.
  • a hydraulic wheel cylinder is fitted to each wheel.
  • hydraulic cylinders may be used only at the front wheels, and the rear wheels may be provided with calipers that provide braking force with the aid of an electric motor.
  • the operation of the actuators for controlling wheel cylinder hydraulic pressure for example, the method for setting motor rotational speed (command value), is not limited to that of the embodiments and may be modified as required.
  • the embodiments may be combined as required.

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  • Engineering & Computer Science (AREA)
  • Transportation (AREA)
  • Mechanical Engineering (AREA)
  • Physics & Mathematics (AREA)
  • Fluid Mechanics (AREA)
  • Regulating Braking Force (AREA)
  • Braking Systems And Boosters (AREA)
US15/300,875 2014-04-24 2014-04-24 Brake control system, brake system, and brake hydraulic pressure generating method Active US10252707B2 (en)

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PCT/JP2014/061521 WO2015162744A1 (fr) 2014-04-24 2014-04-24 Dispositif de commande de frein, système de freinage, et procédé de génération de pression hydraulique de frein

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CN113734122B (zh) * 2021-09-22 2022-07-19 中国第一汽车股份有限公司 一种制动系统的辅助制动控制方法和装置

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KR20160134833A (ko) 2016-11-23
CN106232441A (zh) 2016-12-14
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US20170015293A1 (en) 2017-01-19
WO2015162744A1 (fr) 2015-10-29

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